Microstructure enhanced absorption photosensitive devices

ABSTRACT

Microstructure enhanced photodiodes and avalanche photodiodes are monolithically integrated with CMOS/BiCMOS circuitry such as transimpedance amplifiers. Microstructures, such as holes, can improve quantum efficiency in silicon and III-V materials and can also reduce avalanche voltages for avalanche photodiodes. Applications include optical communications within and between datacenters, telecommunications, LIDAR, and free space data communication.

REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of each U.S. patentapplication Ser. No. 15/309,922 filed Nov. 9, 2016, allowed Jun. 30,2017.

This application also is a continuation-in-part of each of U.S. patentapplication Ser. No. 14/947,718 filed Nov. 20, 2015, and InternationalPatent Appl. No. PCT/US16/67977 filed Dec. 21, 2016 published as WO2017/112747.

This application incorporates by reference, and claims the benefit ofthe filing date of each of the above-identified three patentapplication, as well as of the applications that they incorporate byreference, directly or indirectly, and the benefit of which they claim,including U.S. provisional applications, U.S. non-provisionalapplications, and International applications.

Said application Ser. No. 15/309,922 is a continuation of each of (i)U.S. patent application Ser. No. 14/943,898 (now U.S. Pat. No.9,530,905), (ii) U.S. patent application Ser. No. 14/945,003 (now U.S.Pat. No. 9,525,084), and International Patent Appl. No. PCT/US15/061120,and incorporates each by reference and claims the benefit of the filingdate of each as well as of each of the U.S. Provisional patentapplications the benefit of which they claim.

Said application Ser. No. 14/947,718 is a continuation of InternationalPatent Appl. No. PCT/US14/39208, published as WO 2014/190189, andincorporates each by reference and claims the benefit of the filing datethereof and of each of the U.S. Provisional patent applications thebenefit of which it claims. U.S. application Ser. No. 14/892,821, nowU.S. Pat. No. 9,496,435, is a national stage application of saidPCT/US14/39208.

This patent application claims the benefit of and incorporates byreference each of the following provisional applications:

U.S. Prov. Ser. No. 62/465,734 filed Mar. 1, 2017;

U.S. Prov. Ser. No. 62/474,179 filed Mar. 21, 2017;

U.S. Prov. Ser. No. 62/484,474 filed Apr. 12, 2017;

U.S. Prov. Ser. No. 62/487,606 filed Apr. 20, 2017;

U.S. Prov. Ser. No. 62/488,998 filed Apr. 24, 2017;

U.S. Prov. Ser. No. 62/500,581 filed May 3, 2017;

U.S. Prov. Ser. No. 62/505,974 filed May 14, 2017;

U.S. Prov. Ser. No. 62/509,093 filed May 20, 2017;

U.S. Prov. Ser. No. 62/510,249 filed May 23, 2017;

U.S. Prov. Ser. No. 62/514,889 filed Jun. 4, 2017;

U.S. Prov. Ser. No. 62/521,504 filed Jun. 18, 2017;

U.S. Prov. Ser. No. 62/522,169 filed Jun. 20, 2017;

U.S. Prov. Ser. No. 62/527,962 filed Jun. 30, 2017;

U.S. Prov. Ser. No. 62/530,281 filed Jul. 9, 2017;

U.S. Prov. Ser. No. 62/533,078 filed Jul. 16, 2017;

U.S. Prov. Ser. No. 62/533,603 filed Jul. 17, 2017;

U.S. Prov. Ser. No. 62/535,801 filed Jul. 21, 2017;

U.S. Prov. Ser. No. 62/540,524 filed Aug. 2, 2017;

U.S. Prov. Ser. No. 62/542,243 filed Aug. 7, 2017;

U.S. Prov. Ser. No. 62/547,728 filed Aug. 18, 2017;

U.S. Prov. Ser. No. 62/553,844 filed Sep. 2, 2017;

U.S. Prov. Ser. No. 62/556,426 filed Sep. 10, 2017; and

U.S. Prov. Ser. No. 62/561,869 filed Sep. 22, 2017.

All of the above-referenced provisional and non-provisional patentapplications are collectively referenced herein as “the commonlyassigned incorporated applications.”

FIELD

This patent specification relates mainly to photosensitive devices. Moreparticularly, some embodiments relate to photosensitive devices havingmicrostructure enhanced absorption characteristics.

BACKGROUND

Fiber-optic communication is widely used in applications such astelecommunications, communication within large data centers, andcommunications between data centers. Because of attenuation lossesassociated with using shorter optical wavelengths, most fiber-optic datacommunication uses optical wavelengths of 800 nm and longer. Commonlyused multimode and single mode optical fiber uses wavelengths between800 nm and 1675 nm. A main component of optical receivers used infiber-optic communication system is the photo detector, usually in theform of a photodiode (PD) or avalanche photodiode (APD).

High-quality low-noise APDs can be made from silicon. However, whilesilicon will absorb light in the visible and near infrared range, itbecomes more transparent at longer optical wavelengths. Silicon PDs andAPDs can be made for optical wavelengths of 800 nm and longer byincreasing the thickness of the absorption “I” region of the device.However, in order to obtain adequate quantum efficiency (also known asexternal quantum efficiency), the thickness of the silicon “I” regionbecomes so large that the device's maximum bandwidth (also referred toas “data rate”) is too low for many current and future telecom and datacenter applications.

To avoid the inherent problem that silicon PDs and APDs have with longerwavelengths and higher bandwidths, other materials are used. Germanium(Ge) APDs detect infrared out to a wavelength of 2000 nm, but hasrelatively high multiplication noise. InGaAs APDs can detect out tolonger than 1600 nm, and have less multiplication noise than Ge, butstill far greater multiplication noise than silicon APDs. InGaAs isknown to be used as the absorption region of a heterostructure diode,most typically involving InP as a substrate and as a multiplicationlayer. This material system is compatible with an absorption window ofroughly 900 to 1700 nm. However, both InGaAs PD and APD devices arerelatively expensive and have relatively high multiplication noise whencompared with silicon and are difficult to integrate with Si electronicsas a single chip.

Information published by a major company in the business ofphotodetectors (Seehttp://files.shareholder.com/downloads/FNSR/0x0x382377/0b3893ea-fb06-417d-ac71-84f2f9084b0d/Finisar_Investor_Presentation.pdf,)indicates at page 10 that the current market for optical communicationdevices is over 7 billion U.S. dollars with a compounded annual growthrate of 12%. Photodiodes (PD) used for 850-950 nm wavelength employ GaAsmaterial and for 1550-1650 nm wavelength photodiodes are InP materialbased, which is both expensive and difficult to integrate with Si basedelectronics. Therefore, there is a large market and a long-felt needthat has not been met for the development of a better device. To datethere are no Si material based photodiodes nor avalanche photodiodes(APD) for 850-950 nm and no Ge on Si material based photodiodes noravalanche photodiodes for 1550-1650 nm that are top-surface orbottom-surface illuminated, with a data rate of at least 25 Gb/s, andare monolithically integrated with CMOS/BiCMOS silicon electronics on asingle chip that are commercially available to the knowledge of theinventors herein. However, there has been no lack of trying to develop abetter device for this large market. For example, there have beenproposals for resonant photodiodes fabricated in Si material (seeResonant-Cavity-Enhanced High-Speed Si Photodiode Grown by EpitaxialLateral Overgrowth, Schaub et al., IEEE PHOTONICS TECHNOLOGY LETTERS,VOL. 11, NO. 12, DECEMBER 1999), but they have not reached the knowncommercial market. Other forms of high speed photodiodes in a waveguideconfiguration have been proposed, such as in 40 GHz Si/Ge uni-travelingcarrier waveguide photodiode, Piels et al, DOI 10.1109/JLT.2014.2310780,Journal of Lightwave Technology (incorporated herein by reference);Monolithic germanium/silicon avalanche photodiodes with 340 GHzgain—bandwidth product, NATURE PHOTONICS|VOL 3|JANUARY2009|www.nature.com/naturephotonics (incorporated herein by referenceand referred to herein as “Kang et al. 2009”); High-speed Gephotodetector monolithically integrated with large cross-sectionsilicon-on-insulator waveguide, Feng et al., Applied Physics Letters 95,261105 (2009), doi: 10.1063/1.3279129 (incorporated herein byreference); where light is coupled edge-wise into an optical waveguideand where the absorption length can be 100 um or longer to compensatefor the weak absorption coefficient of Ge at 1550 nm. In thesepreviously proposed waveguide photodiode structures, light propagatesalong the length of the waveguide and the electric field is appliedacross the PIN waveguide such that the direction of light propagationand the direction of the electric field are predominantly perpendicularin this waveguide configuration. Since light in Si travels approximately1000 times faster than the saturated velocity of electrons/holes, awaveguide PD can be 200 microns long for example and the “l” in the PINcan be 2 microns, for example, and achieve a bandwidth of over 10 Gb/s.Such edge coupling of light is costly in packaging as compared tosurface illumination as described in this patent specification, wheredimensions of the waveguide cross section are typically a few microns ascompared to tens of microns for known surface illuminated photodiodes oravalanche photodiodes. Known waveguide PD/APD are often only single modeoptical systems whereas surface illuminated PD/APD described in thispatent specification can be used in both single and multimode opticalsystems. In addition, known waveguide photodiodes are difficult to testat wafer level, whereas surface illuminated photodiodes described inthis patent specification can be easily tested at wafer level. Knownwaveguide photodiodes/avalanche photodiodes are used mostly in specialtyphotonic circuits and in many cases require careful temperature control,which can be costly and inefficient in a hostile data centerenvironment. A top or bottom illuminated Si and Ge on Si or GeSi on SiPD/APD that can be integrated with Si is not known to be commerciallyavailable at data rates of 25 Gb/s or more at wavelengths of 850-950 nm,1250-1350 nm and 1550-1650 nm. In contrast, photodiodes on Si basedmaterial, as described in this patent specification, can bemonolithically integrated with integrated electronic circuits on asingle Si chip, thereby significantly reducing the cost of packaging. Inaddition, the microstructured PD/APD at 850 nm, 1300 nm and 1550 nmnominal wavelengths described in this patent specification can bepredominantly for short haul (short reach), medium haul (reach gap) andlong haul (long reach), distances less than 300 meters, in certain casesless than 2000 meters, in certain cases less than 10000 meters and incertain cases greater than 10000 meters optical data transmission. Themicrostructured PD/APD direction of incident optical beam and theelectric field in the “I” region of a PIN or NIP structure, arepredominately collinear and/or almost collinear. This patentspecification enables such a device and is expected to transform thecurrent data centers to almost all optical data transmission betweenblades, within a blade, between racks and/or between data centers, thatwill vastly increase the data transmission bandwidth capabilities andsignificantly reduce electrical power usage.

The subject matter claimed herein is not limited to embodiments thatsolve any specific disadvantages or that operate only in environmentssuch as those described above. Rather, this background is only providedto illustrate one exemplary technology area where some embodimentsdescribed herein may be practiced.

Each published document referenced in this patent specification ishereby incorporated by reference.

SUMMARY

According to some embodiments, a single-chip device comprises anintegrated combination of a microstructure-enhanced photodetector (MSPD)and an active electronic circuit, both formed on or in a singlesubstrate and configured to receive an optical input that incross-section is substantially continuous spatially at least some oftime, convert the optical input to an electrical output, and process theelectrical output into a processed output. The MSPD on or in said singlesubstrate comprises an intermediate layer, a first layer at one side ofthe intermediate layer, and a second layer at an opposite side of theintermediate layer, wherein: each of the layers comprises Silicon,Germanium, or an alloy thereof; at least one of said layers, or anoverlying covering layer that may be present, has holes intentionallyformed therein, extending in directions transverse to the layers; eachof the first and second layers comprises a doped material; theintermediate layer comprises a material that is less doped than at leastone of the first and second layers or is undoped, wherein the degree ofdoping is the same or different for different positions in theintermediate layer; an input portion configured to concurrently receiveat a plurality of said holes said optical input that has saidsubstantially continuous cross-section; and an output portion configuredto provide said electrical output from the MSPD. The active electroniccircuit on or in said single substrate is configured to process theelectrical output from the MSPD by applying thereto: amplification toform said processed output from the single-chip device; processing otherthan or in addition to amplification to form said processed output fromthe single-chip device; and routing to one or more selecteddestinations. A communication channel on or in said single-chip deviceis configured to deliver the electrical output from the MSPD to theactive electronic circuit.

The active electronic circuit can at least partly extend beyond saidsubstrate, or can be at least partly inside said substrate. An overlyinglayer can be present as a superstrate at one side of said first,intermediate, and second layers, and can contain said holes. The MSPDcan comprises a III-V materials family photodiode. An air-filled volumecan be formed between the substrate and the MSPD. A layer of adielectric material that is in the propagation path of said opticalinput can be provided to cover the holes as well as spaces between theholes. An avalanche region can be provided at one side of the MSPD,forming therewith an avalanche microstructured photodiode (MSAPD). Theholes can be present in said intermediate layer, in at least one of thefirst and second layers, or in each of the three layers. Each of saidfirst and second layers and said intermediate layer has a thickness andat least some of said holes extend through the entire thickness of theintermediate layer and of one of said first layer and second layer andthrough at least a part of the thickness of the other one of said firstand second layers.

At least some of said holes can be shaped as inverted pyramids, can havetriangular sections in planes transverse to said layers, and thevertices of the pyramids of the triangular sections can be within theintermediate layer. The holes can have sidewalls that slope in planestransverse to said layers, and the holes can have plural differentslopes along their inside walls. At least some of said holes on the samesubstrate can differ from each other in at least one of (i) distance bywhich the holes extend in said directions, (ii) shape of the holes, and(iii) spacing of the holes from each other. When the intermediate layerincludes holes, one of the first and second layers can be in the form ofa layer that conformally covers inside walls of the holes as well asspaces between the holes. The holes can be partly or entirely filledwith a dielectric material.

The optical input enters the MSPD through one or both of said first andsecond layers, and each of the first and second layers through which theoptical input enters can be no more than 500 nanometers thick.

At least one of the first layer, the second layer, and the intermediatelayer comprises a material represented by Ge_(x)Si_(1-x), where x isgreater than zero.

The MSPD further comprises ohmic contacts configured for reverse-biasingthe MSPD, and at least one of said ohmic contact can be through a via insaid substrate.

The single-chip device can further comprise a light guide to said MSPDfor directing said optical input thereto, and electrical contacts fromthe active electronic circuit configured to carry said processed outputout of the single-chip device. The light guide can be configured to bendthe optical input from an initial propagation direction to a propagationdirection transverse to said layers.

The single-chip device can have one or more additional MSPD on or in thesame substrate, one or more additional active electronic circuits, andrespective different optical bandpass filters coupled with at least twoof the MSPDs on or in said single substrate, whereby at least two ofsaid MSPDs can be configured to respond to different wavelength rangesthat are within said optical input. The additional active electroniccircuits can comprise one or more transimpedance amplifiers (TIAs) andone or more application specific integrated circuits (ASICs), and any ofthem can comprise CMOS, BiCMOS, and/or bipolar active devices. Thesingle-chip device can be configured into an optical communicationstructure or a light distance and ranging (LIDAR) structure, and caninclude a laser emitter formed on or in said single substrate.

The MSPD in the single-chip device can include a layer of selectedmaterial that is over a side of one of the first and second layersfacing away from the intermediate layer and is configured to reducesheet resistance. In another example, the layer of selected material canbe configured to reflect light that has passed through the intermediatelayer back toward the intermediate layer. In yet another example, adeliberately textured surface is formed at a side of one of said firstand second layers facing away from the intermediate layer. A layer ofmicro-nano structures can be formed at of one of said first and secondfacing, at a surface thereof facing away from the intermediate layer.One or more distributed Bragg reflectors can be formed at one of saidfirst and second layers, at a surface thereof away from the intermediatelayer. An isolation trench between the MSPD and the active electroniccircuit can be included in the single-chip device, and a light shieldlayer can be formed over said active electronic circuit.

The optical input to the MSPD in the single-chip device and theelectrical output from the MSPD can each be modulated at a frequency ofat least 30 Gigabits per second, and the MSPD can operate at quantumefficiency of at least 1.5 times greater than that of a photodetectorthat is otherwise the same but lacks said holes.

According to some embodiments, the single-chip device is hermeticallysealed, for example with a dielectric such as silicon oxide or nitrideand/or a polymer. This may obviate a need for additional hermeticpackaging in practical applications of the single-chip device, such asin data centers.

According to some embodiments, a microstructure-enhanced photodetector(MSPD) configured to convert to an electrical output an optical inputthat in cross-section is essentially continuous spatially at least someof the time, comprises a substrate and a top layer, a bottom layer, andan intermediate layer between the top and bottom layers formed on or inthe substrate, wherein: at least one of the layers has holesintentionally formed therein, extending in directions transverse to thelayers; each of the top and bottom layers comprises a doped material;and the intermediate layer comprises a material that is undoped or isless doped than the top or bottom layer, wherein the degree of doping isthe same or different for different positions in the intermediate layer.The MSPD includes an input portion configured to receive, concurrentlyat a plurality of said holes, said optical input that has saidessentially continuous cross-section; and an output portion configuredto provide said electrical output.

In some embodiments, the top layer is no more than 500 nm thick and theholes are at least in the top layer, an air-filled volume is providedbetween the substrate and the MSPD, a layer of a dielectric material isprovided that is at a surface of said substrate, over the holes andspaces between the holes, and in the path of said optical input.

The MSPD can further include an avalanche region under the MSPD, formingtherewith an avalanche microstructured photodiode (MSAPD).

The holes in the MSPD can be in the intermediate layer, in one of thetop and bottom layers, or through the entire thickness of all threelayers, or through the entire thickness of one of the top and bottomlayers but only partly into the other.

A least some of said holes can be shaped as inverted pyramids, can havetriangular sections in planes transverse to said layers, the vertices ofthe pyramids and triangular sections can be within the intermediatelayer, the holes can have sidewalls that slope in planes transverse tosaid layers, and there can be plural different slopes along inside wallsof the holes. At least some of said holes in the same substrate candiffer from each other in at least one of (i) distance by which theholes extend in said directions, (ii) shape of the holes, and (iii)spacing of the holes from each other.

When the holes extend into the intermediate layer, one of said top andbottom layers can conformally cover inside walls of the holes as well asspaces between the holes. The holes can be partly or entirely filledwith a dielectric material.

At least one of the top and bottom layers and the intermediate layer cancomprise a material represented by Ge_(x)Si_(1-x), where x is greaterthan zero but less than unity, or where x is zero or unity or a valuebetween zero and unity.

The MSPD can further comprise ohmic contacts configured forreverse-biasing the MSPD, and at least one of said ohmic contact can bethrough a via in said substrate. The MSPD can further comprise a lightguide for directing said optical input thereto. The light guide can beconfigured to bend the optical input from an initial propagationdirection to a propagation direction transverse to at least some of saidlayers. The MSPD can further comprise one or more additional MSPDsformed on or in the same substrate, and respective different opticalbandpass filters coupled with respective ones of the MSPDs, whereby atleast two of said MSPDs are configured to respond to differentwavelength ranges that are within said optical input. The plural MSPDson or in the same substrate can be configured into an opticalcommunication structure or a light distance and ranging (LIDAR)structure. The MSPD can further comprise a laser emitter formed on or insaid single substrate.

The MSPD can include a material that is over a side of one of the topand bottom layers facing away from the intermediate layer and isconfigured to reduce sheet resistance, a material that is over a side ofone of the top and bottom layers facing away from the intermediate layerand is configured to reflect light that has passed through theintermediate layer back toward the intermediate layer, a deliberatelytextured surface at a side of one of said top and bottom layers facingaway from the intermediate layer, a layer of micro-nano structuresformed at a side of one of said top and bottom layers facing away fromthe intermediate layer, and/or one or more distributed Bragg reflectorsformed at a surface of one of said top and bottom layers facing awayfrom the intermediate layer.

When one or more active electronic circuits are formed on or in the samesubstrate as the MSPD and coupled to said MSPD to receive saidelectrical output therefrom and process it into a processed output, theresulting combination forms a single-chip integrated circuit configuredto receive said optical input, convert it to said electrical output, andprovide said processed output.

The MSPD is configured to operate when its optical input and electricaloutput are each modulated at a frequency of at least 30 Gigabits persecond, at a quantum efficiency of at least 1.5 times that of anotherwise the same photoconductor lacking said holes.

According to some embodiments, the MSPD is hermetically sealed, forexample with a dielectric such as silicon oxide or nitride and/or apolymer. This may obviate a need for additional hermetic packaging inpractical applications of MSPD, such as in data centers.

According to some embodiments, a method of making amicrostructure-enhanced photodetector (MSPD) configured to convert anoptical input that at least some of the time has a cross-section that isessentially continuous spatially to an electrical output, comprises:providing a substrate and forming on or in said substrate a top layer, abottom layer, and an intermediate layer between the top and bottomlayers, wherein at least one of the layers has holes intentionallyformed therein, extending in directions transverse to the layers, eachof the top and bottom layers comprises a doped material, theintermediate layer comprises a material that is undoped or is less dopedthan the top or bottom layer, wherein the degree of doping is the sameor different for different positions in the intermediate layer. Themethod further includes forming an input portion configured to receive,concurrently at a plurality of said holes, said optical input that hassaid essentially continuous cross-section, and forming an outputconfigured to provide said electrical output.

The step of forming the top layer can comprise limiting the top layer toa thickness of no more than 500 nm, and the step of forming the holescan comprise forming the holes at least in the top layer. The method canfurther include forming an air-filled volume between the substrate andthe MSPD, a layer of a dielectric material that is at a surface of saidsubstrate, over the holes and spaces between holes, and in the path ofsaid optical input, and an avalanche region under the MSPD, formingtherewith an avalanche microstructured photodiode (MSAPD). Forming theholes can comprise including the holes in said intermediate layer, insaid intermediate layer as well as in at least one of the top and bottomlayers, and/or forming the holes in each of the first, second, andintermediate layer.

The method of claim 1, in which each of said top and bottom layers andsaid intermediate layer has a thickness and the forming of the holescomprises extending the holes through the entire thickness of saidintermediate layer and of one of said top layer and bottom layer andthrough at least a part of the thickness of the other one of said topand bottom layers.

The method can include forming at least some of said holes in the shapeof inverted pyramids, with triangular sections in planes transverse tosaid layers, with vertices of the pyramids or triangular sections in theintermediate layer, and/or with plural different slopes along insidewalls of the holes. The forming of holes can comprise forming at leastsome of said holes such that they differ from each other in at least oneof (i) distance by which the holes extend in said directions, (ii) shapeof the holes, and (iii) spacing of the holes from each other.

When the holes extend into the intermediate layer, the method caninclude forming one of the top and bottom layers to conformally coverinside walls of the holes as well as spaces between the holes. Themethod can include partially or entirely filling the holes with adielectric material, and forming at least one of the top layer, thebottom layer, and the intermediate layer of a material represented byGe_(x)Si_(1-x), where x is greater than zero or where x is zero or unityor a value between zero and unity. The method can further compriseforming ohmic contacts configured for reverse-bias the MSPD, forming alight guide to said MSPD for directing said optical input thereto, wherethe light guide can bend the optical input from an initial propagationdirection to a propagation direction transverse to said layers, andforming one or more additional MSPD formed on or in said substrate forreceiving respective optical inputs, and forming respective differentbandpass filters for said optical inputs, thereby configuring differentMSPDs on said substrate to respond to different wavelength ranges thatare within said optical input.

According to some embodiments, the method includes forming one or moreadditional MSPDs in an array on or in the same substrate, said MSPDsbeing configured into an optical communication structure or a lightdistance and ranging structure (LIDAR), forming a laser emitter on or insaid substrate, forming a layer of selected material that is over a sideof one of the top and bottom layers facing away from the intermediatelayers and is configured to reduce sheet resistance and/or to reflectlight that has passed through the intermediate layer back toward theintermediate layer, deliberately texturing a surface at a side of one ofsaid top and bottom layers facing away from the intermediate layer,forming a layer of micro-nano structures formed at of one of said topand bottom layers, at a surface thereof facing away from theintermediate layer, and/or forming one or more distributed Braggreflectors at one of said top and bottom layers, at a surface thereofaway from the intermediate layer.

According to some embodiments, the method further includes forming, onor in the same substrate as the MSPD, one or more active electroniccircuits configured to process the electrical output from the MSPD intoa processed output, thereby forming a single-chip integrated circuitconfigured to receive said optical input, convert it to said electricaloutput, and provide said processed output.

According to some embodiments, the method further includes hermeticallysealing the MSPD and/or the single-chip device, for example with adielectric such as silicon oxide or nitride and/or a polymer. This mayobviate a need for additional hermetic packaging in practicalapplications of the single-chip device and/or the MSPD, such as in datacenters.

BRIEF DESCRIPTION OF THE DRAWINGS

To further clarify the above and other advantages and features of thesubject matter of this patent specification, specific examples ofembodiments thereof are illustrated in the appended drawings. It shouldbe appreciated that these drawings depict only illustrative embodimentsand are therefore not to be considered limiting of the scope of thispatent specification or the appended claims. The subject matter hereofwill be described and explained with additional specificity and detailthrough the use of the accompanying drawings in which:

FIGS. 1A-1H are top-view scanning electron micrographs of invertedpyramid holes used in a microstructure high speed photodiode (MSPD)and/or a high speed microstructure avalanche photodiode (MSAPD),according to some embodiments;

FIGS. 2A-2D are cross-section scanning electron microscope (SEM)micrographs of holes that are first wet etched using KOH and then dryetched using deep reactive ion etching (DRIE), according to someembodiments;

FIG. 3 is a schematic cross section of a N-I-P photodiode structure thatcan be grown on a silicon substrate or a SOI substrate, according tosome embodiments;

FIG. 4 is a cross sectional schematic drawing of a possible MSPD usingthe layers shown in FIG. 3, according to some embodiments;

FIG. 5 is a schematic cross section of a MSPD with N-I(N⁻)-P structureon P silicon substrate or SOI substrate where the microstructure holeshave an initial funnel followed by a more cylindrical hole, according tosome embodiments;

FIGS. 6A-6D are diagrams illustrating forming of silicon on holes (SOH),according to some embodiments;

FIG. 6E is a cross sectional schematic diagram showing the device inFIG. 5 fabricated on a substrate SOH (silicon on holes), according tosome embodiments;

FIG. 7A is a top view of GeSi and/or Ge on silicon, according to someembodiments;

FIG. 7B is a top view of a spherical grid pattern of GeSi and/or Ge onsilicon, according to some embodiments;

FIG. 7C shows three examples of nano/micro structure holes filled orpartially filled with GeSi and/or Ge, according to some embodiments;

FIG. 8 is a diagram illustrating a monolithically integrated singlesilicon chip that can include single and/or multiple combinations ofdevices, according to some embodiments;

FIGS. 9A and 9B are schematic cross sections of a possible MSPD P-I-Nstructure, according to some embodiments;

FIG. 10 is a cross section view of three funnel shaped holes, accordingto some embodiments;

FIG. 11 is a plot showing a FDTD (Finite Difference Time Domain)simulation for the optical field in a structure as shown in FIG. 10;

FIG. 12A is a plot of a FDTD simulation of a hexagonal lattice withholes given in FIG. 10 where the holes are funnel shaped with a funnelslope of 61 degrees;

FIG. 12B is a plot showing the QE of a MSPD as in curve 1216 of FIG.12A;

FIG. 13 is a plot showing the enhanced absorption vs. wavelength from800-900 nm for an all silicon structure shown in FIG. 10;

FIG. 14 is a cross section schematic of a MSPD monolithically integratedwith CMOS/BiCMOS electronics in a single chip, according to someembodiments;

FIG. 15 is a plot of a FDTD simulation of absorption for a structuresimilar to FIG. 10;

FIG. 16 is a plot of a FDTD simulation of a structure similar to that ofthe plot in FIG. 15 except with a thinner top layer;

FIG. 17 is a plot of a FDTD simulation of a structure similar thatplotted in FIG. 15 except with P and N layers being 100 nm thickness;

FIG. 18A-18E are schematic diagrams of microstructured holes positionedon a photosensitive surface of a MSPD/MSAPD, according to someembodiments;

FIGS. 19A-19D are a series of cross section views illustrating holesbeing etched into a buried oxide layer of a SOI wafer, according to someembodiments;

FIGS. 19E-19H are a series of cross section views illustrating showsholes etched into the oxide of a SOI wafer that are filled with a highindex dielectric, according to some embodiments;

FIG. 19I is a diagram showing a silicon wafer having hole patternsetched for bandpass filtering in locations where MSPDs/MSAPDs are to befabricated, according to some embodiments;

FIG. 20 is a cross sectional diagram showing several filters, eachhaving a different passband for each of several MSPDs, according to someembodiments;

FIG. 21 is a simple schematic diagram showing MSPD/MSAPD arraysmonolithically integrated with CMOS and/or BiCMOS electronics, accordingto some embodiments;

FIGS. 22A and 22B are diagrams illustrating cost savings from using amonolithically integrated MSPD(s)/MSAPD(s) with ASIC(s);

FIG. 23 is a simple schematic diagram showing MSPDs/MSAPDs in an array,according to some embodiments;

FIGS. 24 and 25 are schematic cross section views of a MSAPD with holesthat can have various shapes, according to some embodiments;

FIG. 26 is schematic diagram illustrating integration of the MSAPDstructure in FIG. 24 with CMOS and/or BiCMOS electronics, according tosome embodiments;

FIG. 27 is schematic diagram illustrating integration of the MSAPDstructure in FIG. 24 with CMOS and/or BiCMOS electronics, according tosome other embodiments;

FIG. 28 is a table showing experimental measurements of a MSPD withapproximately 1000 nm thick I layer, 200 nm N layer and approximately1500 nm P layer on 2000 nm BOX on silicon substrate, according to someembodiments;

FIG. 29 is a schematic drawing of a vertical cavity surface emittinglaser (VCSEL) being used together with a MSPD/MSAPD that ismonolithically integrated with ASIC CMOS and/or BiCMOS electronics forclose proximity free space optical data link, according to someembodiments;

FIG. 30 is a cross section view of a basic epitaxial layer structure formonolithic integration of a MSPD with ASICs such as a TIA, according tosome embodiments;

FIG. 31 is a cross section view showing some aspects of a MSPDintegrated with CMOS/BiCMOS ASICs, according to some embodiments;

FIG. 32 is a diagram showing a monolithically integrated MSPD with TIAand other ASICs that is flip chip mounted on a printed circuit boardusing solder bump technology, according to some embodiments;

FIG. 33 is a diagram showing a similar structure to FIG. 30 but withselective P layer growth, diffusion and/or ion implantation on parts ofthe I layer surface, according to some embodiments;

FIG. 34 is a cross section view showing some aspects of a MSPDintegrated with TIA/ASICs using a layer structure as in FIG. 33,according to some embodiments;

FIG. 35 is a cross section view showing an epitaxial layer structure foran MSAPD monolithically integrated with CMOS/BiCMOS ASICs, according tosome embodiments;

FIG. 36 is a cross section view showing some aspects of a MSAPDmonolithically integrated with CMOS/BiCMOS TIA/ASICs, according to someembodiments;

FIG. 37 is a top view showing some aspects of a MSPD/MSAPDmonolithically integrated with a TIA/ASICs without the solder bumpsand/or bond pads, according to some embodiments;

FIG. 38 is cross section view showing some aspects of a MSPD/MSAPDmonolithically integrated with a TIA/ASICs, according to someembodiments;

FIG. 39 is a cross section view an epitaxial layer structure, accordingto some embodiments;

FIG. 40 is a cross section view illustrating some aspects of MSPD-ASICmonolithic integration, according to some embodiments;

FIG. 41 is a cross section view illustrating some further aspects ofMSPD-ASIC monolithic integration, according to some embodiments;

FIG. 42 is a cross section view illustrating aspects of MSPDmonolithically integrated with CMOS/BiCMOS electronics, according tosome embodiments;

FIG. 43 is a cross section view of a structure similar to FIG. 41 exceptthat the holes are etched through the P-I-N structure, according to someembodiments;

FIGS. 44A-44C are cross section views illustrating some further aspectsof MSPD-ASIC monolithic integration, according to some embodiments;

FIG. 45 is a cross section view as in FIGS. 44A-44C illustrating somefurther aspects of MSPD-ASIC monolithic integration, according to someembodiments;

FIG. 46 is a cross section view illustrating some further aspects ofMSPD-ASIC monolithic integration, according to some embodiments;

FIG. 47 is a cross section view illustrating some further aspects ofMSPD-ASIC monolithic integration, according to some embodiments;

FIG. 48 is a cross section view illustrating some further aspects ofMSPD-ASIC monolithic integration similar to FIG. 47, according to someembodiments;

FIGS. 49, 50A and 50B are top views and a cross section viewillustrating some aspects of selective ion implantation for MSPD-ASICmonolithic integration, according to some embodiments;

FIG. 51 is a cross sectional view of a microstructured avalanchephotodiode (MSAPD) with a P⁺ P⁻⁻PN⁺ structure on SOI wafer, according tosome embodiments;

FIG. 52 is a cross section view of a MSAPD integrated with CMOS/BiCMOSICs such as TIA and other ASICS for signal processing, according to someembodiments;

FIG. 53 is a top view schematic of an array of MSPDs/MSAPDs integratedwith CMOS/BiCMOS ICs such as TIA and other signal processing ASICs,according to some embodiments;

FIG. 54 is a cross section of a possible layer structure for integratingMSPD/MSAPD with CMOS/BiCMOS electronics, according to some embodiments;

FIG. 55 is a cross section view illustrating some aspects of MSPD/MSAPDintegration with CMOS/BiCMOS integrated circuits, according to someembodiments;

FIG. 56 is a cross section view illustrating some aspects of MSPD/MSAPDintegration with CMOS/BiCMOS integrated circuits, according to someembodiments;

FIG. 57 is cross section view of a CMOS/BiCMOS wafer on SOI for use inintegration with MSPDs/MSAPDs, according to some embodiments;

FIG. 58 is cross section showing some aspects CMOS/BiCMOS integrationwith MSPDs/MSAPDs, according to some embodiments;

FIGS. 59A and 59B are cross sections illustrating some aspects of a MSPDintegrated with CMOS/BiCMOS ASICs that include a TIA on a CMOS/BiCMOScompatible silicon substrate, according to some embodiments;

FIG. 60 is a cross section view of a silicon PIN photodiode integratedwith TIA and other ASICs, according to some embodiments;

FIGS. 61A-61D are top views illustrating aspects of microstructuredoptical waveguides, according to some embodiments;

FIG. 62A is a cross section view showing aspects of a microstructuredoptical waveguides photodiode (MSOWPD) integrated with CMOS/BiCMOSASICs, according to some embodiments;

FIGS. 62B and 62C are top views showing further aspects ofmicrostructured optical waveguides photodiodes according to someembodiments;

FIGS. 63A-63C are cross section views illustrating aspects of MSPDsintegrated with CMOS/BiCMOS circuitry utilizing selective area growth ofGe and/or GeSi on silicon, according to some embodiments;

FIG. 64 is a cross section view showing aspects of aMSPD/MSAPD/MSOWPD/MSOWAPD having surface microstructures and ismonolithically integrated with CMOS and/or BiCMOS ICs, according to someembodiments;

FIGS. 65, 66 and 67 are cross sectional views showing aspects ofmonolithically integrated MSPDs and CMOS/BiCMOS ICs with a throughsilicon via (TSV), according to some embodiments;

FIG. 68A is a cross section showing a layer structure of Ge and/or GeSion Si for monolithic integration of an MSPD with CMOS/BiCMOS ASICs,according to some embodiments;

FIG. 68B is a cross section showing some further aspects of amonolithically integrated CMOS/BiCMOS ASICs with a MSPD using a Geand/or GeSi on Si, according to some embodiments;

FIGS. 69A and 69B are cross section views showing some aspects ofmonolithic integration of a MSPD with CMOS/BiCMOS ASICs, according tosome embodiments;

FIG. 70A is a cross section illustrating some aspects of integration ofa MSPD with CMOS/BiCMOS ASICs, according to some embodiments;

FIG. 70B is a plot showing absorption for an MSPD simulated using usingfinite difference time domain analysis (FDTD), according to someembodiments;

FIG. 70C is a plot showing a FDTD simulation of the optical field in themicrostructure holes, according to some embodiments;

FIG. 70D is a plot of a data rate bandwidth calculation, according tosome embodiments;

FIG. 71 is cross section view similar to FIG. 70A with the addition of aBOX (buried oxide) layer;

FIG. 72 is a cross section showing some aspects of a MSAPDmonolithically integrated with CMOS/BiCMOS ICs, according to someembodiments;

FIG. 73 is a cross section view of a structure that is similar to thatof FIG. 72 except that a buried N type device layer is included;

FIGS. 74 and 75 are perspective views showing some aspects of aconnecting wells for connecting surface electrodes to lower layers,according to some embodiments;

FIGS. 76A to 76K are diagrams illustrating aspects of a basic processflow for fabricating MSPDs monolithically integrated with CMOS/BiCMOSASICs, according to some embodiments;

FIG. 77A is cross section view of an MSPD, according to someembodiments;

FIG. 77B is a plot showing a FDTD simulation of the optical fieldspanning wavelengths from 800 nm to 900 nm interacting withmicrostructure holes, according to some embodiments;

FIG. 78 is a cross section view of a structure similar to FIG. 76A witha BOX layer (or on a SOI wafer), according to some embodiments;

FIG. 79 is a plot showing a FDTD simulation of the structure shown inFIG. 78 of the optical field interacting with the microstructure holesin silicon;

FIG. 80 is a cross section illustrating some aspects of a MSAPD withmicrostructure holes, according to some embodiments;

FIG. 81 is a cross section similar to FIG. 80, and illustrating someaspects of a MSAPD with microstructure holes, according to someembodiments;

FIGS. 82A and 82B are cross sectional views of layer structures prior tointegration of a MSPD with CMOS/BiCMOS ASICs, according to someembodiments;

FIG. 83 is a cross section view showing aspects of a starting layerstructure with N⁺ surface well, according to some embodiments;

FIGS. 84A and 84B are cross sectional views of a MSPD/MSAPD on SOIand/or a sacrificial layer, according to some embodiments;

FIG. 85 is a top view of a MSPD/MSAPD integrated with CMOS/BiCMOS,according to some embodiments;

FIG. 86 is a plot showing the results of a FDTD simulation of theoptical field on inverted pyramid holes on 1 micron thick silicon withair interfaces on both the top and bottom;

FIG. 87 is a cross section view of a N-I-P photodiode structure on SOIwith a BOX layer, according to some embodiments;

FIG. 88 is a plot showing a FDTD simulation of absorption of theincident photons in the I or low doped layer as a function of wavelengthfrom 800-900 nm for the structure shown in FIG. 87;

FIG. 89 is a cross section view of an MSPD, according to someembodiments;

FIG. 90 is a cross section view of a MSPD PIN structure that can bemonolithically integrated with CMOS/BiCMOS ASICs on a SOI wafer,according to some embodiments;

FIG. 91 is a plot showing a FDTD simulation of the optical field from800-900 nm wavelength impinging on the top surface of a structure shownin FIG. 90;

FIG. 92 is a cross section view of a two-dimensional (2D) materialphotodetector that can have an absorption enhancement by employing microand/or nano holes for photon trapping, according to some embodiments;

FIG. 93 is a cross section view of a MSPD PIN structure similar to thatshown in FIG. 90, according to some embodiments;

FIG. 94 is cross section showing a structure similar to FIG. 80 exceptwith the addition of a superstrate as shown in FIG. 93;

FIGS. 95A to 95C are plots showing a FDTD simulation of the opticalfield absorption in the I or low doped layers of FIGS. 93 and 94;

FIG. 96 is a cross section view of a lateral P-I-N photodiode structurethat is surface illuminated, according to some embodiments;

FIG. 97 is a top view of the structure shown in FIG. 96, according tosome embodiments;

FIG. 98 is a top view of an integrated MSPD/MSAPD, according to someembodiments;

FIG. 99A is a cross section schematic of a microstructure enhanced III-Vphotodiode, according to some embodiments;

FIG. 99B is a plot showing an FDTD simulation of the the structure shownin FIG. 99A;

FIG. 100 is a cross section of a MSPD, according to some embodiments;and

FIG. 101 is a cross section of a MSPD (or MSAPD) with a mesa and theregions under the microstructure holes selectively removed, according tosome embodiments;

FIG. 102 is a plot showing an FDTD simulation of the optical fieldabsorption enhancement verses wavelength for a MSPD structure and witheither a PIPN or PIPIN structure for a MSAPD device, according to someembodiments; and

FIG. 103 is a cross section of an MSPD or MSAPD having Ge and/or GeSilayers grown on Si that is monolithically integrated with CMOS/BiCMOSASICs, according to some embodiments.

DETAILED DESCRIPTION

A detailed description of examples of preferred embodiments is providedbelow. While several embodiments are described, it should be understoodthat the new subject matter described in this patent specification isnot limited to any one embodiment or combination of embodimentsdescribed herein, but instead encompasses numerous alternatives,modifications, and equivalents. In addition, while numerous specificdetails are set forth in the following description in order to provide athorough understanding, some embodiments can be practiced without someor all of these details. Moreover, for the purpose of clarity, certaintechnical material that is known in the related art has not beendescribed in detail in order to avoid unnecessarily obscuring the newsubject matter described herein. It should be clear that individualfeatures of one or several of the specific embodiments described hereincan be used in combination with features or other described embodiments.Further, like reference numbers and designations in the various drawingsindicate like elements.

Microstructures in photodiodes and microstructures avalanche photodiodescan enhance the absorption of incident signal photons and can result ina larger external quantum efficiency over a similar structure withoutmicrostructures for enhancement of the absorption over a givenwavelength range. Enhancement of the absorption can also be viewed as anenhancement in the absorption length. Light can interact with absorbinglayer(s) for a longer length of time, which if velocity is constant canequivalently be longer distance. The optical modes excited in amicrostructured photodiode/avalanche photodiode can propagate in adirection that is the same and/or different from the incident photondirection impinging in the microstructured photodiode/avalanchephotodiode (MPD/APD) which can include a predominantly lateral directionin the plane of the epitaxial layers and/or a mixture of lateral andvertical stationary and/or propagating optical modes. The optical modescan be any arithmetic combination of vertical and lateral modes whichare complex coupled modes of many resonators that may be similar and/ordifferent. In addition, slow waves can be generated by themicrostructures that further enhance absorption and therefore quantumefficiency (external quantum efficiency where reflection off theincident surface and transmission through the structure and anyscattering can be accounted for, when quantum efficiency is mentioned itis always the external quantum efficiency) which is proportional toabsorption in the case of photodiodes. Ratios of quantum efficiency toabsorption can range from 1 to 0.3, for example. For a heterostructurephotodiode, for example a P-I-N structure where the P and N are siliconand the I can be GeSi alloy, at longer wavelengths, for example, 950 nmor longer, the P and N will absorb less and most of the absorption willoccur in the I GeSi layer. This can result in a quantum efficiency toabsorption ratio closer to 1, for example 0.6-0.99. In the case ofavalanche photodiode where there is gain, quantum efficiency can oftenbe greater than 100%; for example with an absorption of 60% and a ratioof quantum efficiency to absorption ratio of 70% (in the case of unitygain) the quantum efficiency is 42% and with a gain of 2 (3 dB) thequantum efficiency can be 84% and with a gain of 4 (6 dB) the quantumefficiency can be 164%.

The microstructured photodiodes and microstructured avalanchephotodiodes are predominantly surface illuminated where the opticalsignal impinges on either the top or bottom or both surfaces of thephotodiode/avalanche photodiode. The angle of the incident photon,depending on the numerical aperture and/or angle of the fiber, can rangein angles from 80 degrees off normal to normal.

The microstructure holes can be etched in a KOH solution, see Refs. Fanet al, Differences in etching characteristics of TMAH and KOH onpreparing inverted pyramids for silicon solar cells, Applied SurfaceScience 264 (2013) 761-766; and Mavrokefalos et al, Efficient LightTrapping in Inverted Nanopyramid Thin Crystalline Silicon Membranes forSolar Cell Applications, Nano Lett. 2012, 12, 2792-2796 (bothincorporated herein by reference).

In addition, holes can be etched with any combinations of wet and dryetching and also can have a multiple of wet/dry/wet/dry/wet etchings todefine different hole shapes, different features such as nano glass toreduce reflections, and different wet and dry etching methods andchemicals.

FIGS. 1A-1H are top-view scanning electron micrographs of holes in theshape of inverted pyramids used in a microstructure high speedphotodiode (MSPD) and/or a high speed microstructure avalanchephotodiode (MSAPD), according to some embodiments. The microstructureswere etched using a KOH anisotropic etch for holes ranging in diagonalfrom 250 nm to 700 nm and period ranging from 500 nm to 1000 nm. In somecases, the hole diameters can range from 200 nm to 2500 nm and periodscan ranging from 300 nm to 3000 nm. An etch depth of 0.5-1.2 microns isshown, depending on hole diameter or diagonal. In some cases, etch depthcan range from 0.2 to 10 microns for example. These microstructuresresemble invented pyramids. Inverse pyramids are illustrated in Zhang etal, Silicon single-photon avalanche diodes with nano-structured lighttrapping, Nature Communications, 8:628, published online 20 Sep. 2017(DOI 10:1038/s41467-017-00733-y, www.nature.com/naturecommunications).The stated publication date of this paper is later than the filing datesof all but the most recent of the provisional applications the benefitof which this patent specification claims directly. While there aresignificant differences between the paper and the embodiments describedin this patent specification, the paper can be considered a confirmationof benefits of inverted (inverse) pyramids illuminated by a beam oflight.

FIGS. 2A-2D are cross-section scanning electron microscope (SEM)micrographs of holes that are first wet etched using KOH and then dryetched using deep reactive ion etching (DRIE), according to someembodiments. See e.g., Wu et al, High aspect ratio silicon etch: Areview, J. Appl. Phys. 108, 051101 L2010 (incorporated herein byreference and referred to herein as “Wu et al”). Some nano-grass canalso appear after dry etching due to any contaminants such as flakes ofsilicon nitride etch mask, that may be on the surface of the holes afterthe wet etch. The nano-grass can help reduce reflections and improve theenhancement of absorption and therefore the quantum efficiency. Thenano-grass can also be removed by further wet etching. Cycles of wet anddry etching can be repeated to generate the desired hole profile foroptimizing the absorption enhancements over a certain wavelength range,spanning from a few nanometers to tens of nanometers to hundrednanometers or more. In FIGS. 1A-1H and 2A-2D the material is silicon forwavelength ranges from 800 nm to 980 nm and in some cases from 840 nm to960 nm and in some cases from 850 nm to 950 nm. According to someembodiments, the material can be germanium in silicon, Ge_(x)Si_(1-x),where x can range from 0 to 1, and in some cases 0.01 to 0.1 and in somecases from 0.1 to 0.2 and in some cases from 0.2 to 0.4 and in somecases from 0.4 to 0.8. With the addition of Ge and if the layers are notrelaxed, or with strain, the wavelength range can be extended beyond 900nm, in some cases beyond 1000 nm, in some cases beyond 1200 nm, in somecases beyond 1400 and in some cases beyond 1550 nm. In all cases thewavelength range is above the bandgap energy of the GeSi alloy withstrain which can further reduce the bandgap energy, and in some caseswithout strain. The quantum efficiency can range from 40% to 90% or morein at least one wavelength in these wavelength ranges, and in some casesfrom 50% to 80% or more and in some cases from 60% to 80% or more.

Microstructure enhancement of the absorption where the bulk absorptionwithout micro/nano-structures can be in the range of a few hundred cm⁻¹,can range from 2 to 10, in some cases from 10 to 50, in some cases 50 to100 and in some cases more than a 100 times in either Si and/or GeSialloys PIN, PIPIN photodiode and/or avalanche photodiode structures. Insome cases, a strongly absorbing layer of 8000 cm⁻¹ or more can be verythin, for example 1 micron or less, such that the absorption can be weakand microstructure holes can enhance the absorption. In these cases, theincident photons can be mostly collinear with the electric field in theI region. However once the optical field is trapped in themicrostructures and propagates within the microstructure and itsproximity, the optical mode and field can be very complex and may havesome components that may be collinear with the applied electric field inthe I region.

FIG. 3 is a schematic cross section of a N-I-P photodiode structure thatcan be grown on a silicon substrate or a SOI substrate, according tosome embodiments. The I layer can be intrinsic (I) not intentionallydoped and/or very low background with a N type doping N⁻. In some casesit can be very low background P type doping P⁻. In FIG. 3, the I or N⁻layer is Ge_(x)Si_(1-x) alloy with x ranging from greater than 0 to 1,for example for a few percent of x, 1-10% or more, and in some cases4-8% and in some cases 10-20%, and in some cases 20-40% or more. Due tolattice mismatch between GeSi alloy and Si, a strain is created that canresult in a electric field that can assist the transport of electronhole pairs that are generated by photoabsorption. The strain also cannarrow the bandgap of the GeSi alloy. By taking advantage of the strainelectric field in the same direction as a reverse bias electric field,the photogenerated carriers can be more effectively swept through the Ior low doped regions to generate an electrical signal in the externalcircuits attached to the anode and cathode of the photodiode and/oravalanche photodiode.

FIG. 4 is a cross sectional schematic drawing of a possible MSPD usingthe layers shown in FIG. 3, according to some embodiments. The top N⁺layer can have a thickness of 0.1-0.5 microns and doping in the range ofgreater than 5×10¹⁸ cm⁻³, and in some cases greater than 2×10¹⁹ cm⁻³ ofphosphorous and/or arsenic for example. A thin layer of transparentconducting oxide and/or metal can also be included on top of the N⁺layer to further reduce the sheet resistance. The N⁺ layer can be SIand/or GeSi with thickness ranging from 0.1 to 0.5 microns and withdoping greater than 2×10¹⁹ cm⁻³. The I intrinsic layer, or the very lowdoped N⁻ (or P⁻) layer can have a thickness ranging from 0.5-3 microns,and in some cases 1.8-2.2 microns, can have a background doping of lessthan 5×10¹⁵ cm⁻³ and in some cases less than 2×10¹⁵ cm⁻³. The I or N⁻layer can be Ge_(x)Si_(1-x) with x between greater than 0 and less thanor equal to 1. The bottom P layer can be Si and/or GeSi alloy, withthickness ranging from 0.1 to 0.5 microns with doping greater than5×10¹⁹ cm⁻³ and in some cases greater than 1×10²⁰ cm⁻³ with boron and/oraluminum for example. Other dopants may be used in the periodic tablefor P and N such as carbon, antimony, to name a few but these are lesscommon and seldom used in CMOS processing. The N-I-P layers can be grownon a silicon substrate that can be either P or N doping, or on a SOI(silicon on insulator) substrate with a device layer of either P or N.Microstructure holes 412 are etched into the N-I-P (or P-I-N, orP-I-P-I-N for MSAPDs) structure using both wet anisotropic etch,isotropic etch and dry etching such as DRIE, ICP (inductive coupledplasma), HAR (high aspect ratio) etching as in Wu et al. A mixture ofwet and dry etching can be used with a final wet etch to remove any dryetching damage to the Si, GeSi. Hole dimensions, diameter, diagonal,sides, major and minor semi-axis, can range from 200 nm to 3000 nm andin some cases 400 nm to 2000 nm and in some cases from 500 nm to 1800nm, and spacing between the micro/nano structures can be periodic,aperiodic and/or any combination or periodic and aperiodic; the spacingcan range from 0 nm (touching and/or intersecting) to 5000 nm, and insome cases 100 nm to 3000 nm and in some cases 100 nm to 2000 nm and insome cases 100 nm to 1500 nm. The spacing in the lateral directions,such as the x and y directions on a plane for example, can be differentand/or the same, can be periodic and/or aperiodic and/or any combinationof periodic and aperiodic. Other geometries such as hexagonal, thedistance to the nearest neighbor holes can be same or different and canbe periodic and/or aperiodic and/or any combination of periodic andaperiodic. Hole dimension can also be different and/or the same asadjacent holes, hole etch depth can also be different and/or the same,hole depth can range from 0.2 microns to 10 microns. As shown in FIG. 4,the holes 412 can be trapezoidal, and/or can have any number of slopesof its sidewalls and can be etched within the top N or P layer,partially into the I layer, through the I layer, partially into thebottom P or N layer, through the P or N layer to the silicon dioxidelayer of a SOI wafer for example or to an etch stop layer in a bulksilicon substrate for example.

Light impinges from the top layer at an angle normal to 50 degrees offnormal. The MSPD is operated at a reverse bias voltage applied betweenthe anode and cathode, ranging from −1 to −10 volts and for a MSAPD, areverse bias voltage is applied between the anode and cathode rangingfrom −4 to −45 volts. Electrical signal is extracted via the anode 420and cathode 422 connected to a transmission line that in turn isconnected to signal processing and biasing circuits which can bemonolithically integrated with the MSPD/MSAPD into a single chip.

The wavelength range, depending on the percentage of Ge in Si, for 0% Gecan range from 840-960 nm, and with 10% Ge or less in GeSi alloy that iseither relaxed or not relaxed, the wavelength can range from 840-990 nmfor not relaxed GeSi layer and 840-960 nm for relax, for 20% or less Ge,the wavelength can be extended to 1000 nm and in some cases to 1250 nmfor not relaxed GeSi layer and for 40% or less Ge, the wavelength can beextended to 1310 nm. Depending on the amount of strain, the bandgapnarrowing of GeSi alloy can vary over a wider or narrower range ofwavelengths. Quantum efficiency can be 40% or more at at least one ormore wavelengths in the wavelength range.

With zero external bias, the MSPD with strained GeSi layer can operatein a photovoltage mode and it can be seen that the addition of straincan result in an electric field that can assist in the collection ofphotogenerated carriers between the N and P regions that can result in ahigher quantum efficiency for the photovoltaic cell; quantum efficiencygreater than 25% and in some cases greater than 28% under one sun at sealevel, air mass 1 (AM1).

FIG. 5 is a schematic cross section of a MSPD with N-I(N⁻)-P structureon P silicon substrate or SOI substrate where the microstructure holeshave an initial funnel followed by a more cylindrical hole, according tosome embodiments. The shapes of holes 512 can be accomplished by acombination of wet and dry etching, see FIG. 2. The layer structures,microstructure hole dimensions, depth can be similar to those in FIG. 4,with the addition of additional micro/nano structure holes 532 that areetched from the bottom substrate that may or may not include a SOI. Thesubstrate can be thinned from its usual 600-700 microns thickness tounder 200 microns for example. These bottom holes 532 can be photoniccrystal in design to provide a reflectivity of optical waves thatimpinge from the top surface back toward the light trapping micro/nanostructures for absorption enhancements and therefore the enhancement ofthe quantum efficiency. Also, the bottom holes 532 can provide a lowereffective refractive indices such that optical signal from the top canbe reflected back toward the photon trapping structures. The bottomholes can have any shape, periodic and/or aperiodic and the etch depthcan be to the bottom P layer, before the bottom P layer and/or partiallyinto the bottom P layer. The bottom holes can have shapes ofcylindrical, pyramidal, trapezoidal, polygonal, rectangular, oval, andany combination of shapes and dimensions.

FIGS. 6A-6D are diagrams illustrating forming of silicon on holes (SOH),according to some embodiments. The SOH can be formed where the bottomholes 632 can be formed first on a different substrate (FIG. 6B) andsubsequently wafer bonded to another wafer using SOI manufacturingmethods (FIG. 6C). See, e.g., Singh et al, SILICON ON INSULATORTECHNOLOGY REVIEW, International Journal of Engineering Sciences &Emerging Technologies, May 2011, Volume 1, Issue 1, pp: 1-16 ©IJESET(incorporated herein by reference and referred to herein as “Singh”),discussing holes similar to silicon dioxide can be buried and theMSPD/MSAPD/CMOS, BiCMOS layers can be grown to the buried hole devicelayer. The basic steps consist of etching holes in a device wafer thatcan include epitaxial layers that can include doped P and/or N and/or Ilayers, SOI, additional dielectric coatings, metallic layers/fillers,graphene, ceramic, amorphous semiconductor, transparent conductingoxides, spin on glass to name a few, and can be periodic, aperiodic, andany combination of periodic and aperiodic, different and/or samedimensions, different and/or same shaped holes, different and/or samespacings with its nearest neighbor holes. The holes 632 can be filledwith gas such as He, Ar, N, Xe, H, to name a few. In addition the holescan be over the entire wafer and/or over only partial of the waferand/or any patterns on the wafer. The holes 632 in addition to differentdimensions can also have different depths. Alignment registration holescan be included such that different devices can be positioned overdifferent hole patterns for that particular functionality. The waferwith holes or any other patterns of voids is then flipped over and waferbonded to a handle wafer which can include etch stop layers, devicelayers such as PN junctions, P-I-N or N-I-P layers, and/or any otherlayers for device fabrication. It can also include ion implanted layerssuch as H, N, Ar, Xe, Ni, Al, B, As, P, Ga, In, Ge, Si, V, He, Mg, Mn,and/or other elements in the periodic table. Using techniques developedfor SOI manufacturing, the device wafer is cut and chemical mechanicalpolished (CMP) (FIG. 6D) and is ready for growth of further devicelayers such as MSPD, MSAPD, CMOS and/or BiCMOS for application specificintegrated circuits (ASIC), and other structures such as microwavetransmission lines, microwave devices, light emitting diodes, lasers,surface emitting lasers to name a few for monolithic integration into asingle silicon chip.

FIG. 6E is a cross sectional schematic diagram showing the device inFIG. 5 fabricated on a substrate SOH (silicon on holes), according tosome embodiments. Using similar methods as SOI manufacturing, the oxidelayer is replaced by holes 632 that are etched and then bonded to ahandle wafer and using SmartCut (as described in Singh) a thin devicelayer above the holes can be formed and with subsequent chemicalmechanical polishing the surface of the device layer can be used forsubsequent epitaxial layer growth to fabricate MSPD, MSAPD, CMOS,BiCMOS, lasers, surface emitting lasers, microwave transmission lines,solar cells, and any other optical, electrical, mechanical, chemical,devices, sensors for example. All the MSPD, MSAPD, monolithicintegration with CMOS, BiCMOS mentioned in this application can befabricated on a SOH wafer, in addition to SOI and bulk wafers.

FIG. 7A is a top view of GeSi and/or Ge on silicon, according to someembodiments. The GeSi and/or Ge can have a top layer of Si and/or GeSi.Due to the lattice difference between the GeSi and/or Ge on Si, thewafer tends to bow after the growth of GeSi and/or Ge on Si layers onsilicon wafer, especially for thick layers of GeSi and/or Ge of 1-3micron range and in some cases 0.5-2 micron range in the case where theGeSi and/or Ge is not relaxed and under strain. For photodetectors, itcan be desirable for the GeSi and/or Ge to be under strain as this tendsto narrow the bandgap (in lasers strain tend to increase the gain),thereby extending the usable wavelength further into the infrared.However, the bowing of the wafer can be undesirable in high volumemanufacturing as many machines used in manufacturing require wafers tobe flat or at least with minimal bowing. To remove the overall stain andjust allow local strain, a grid pattern in a Manhattan geometry, shownin FIG. 7A, can be etched or in any other pattern such that strain isonly at local areas. Material can be etched to the Si layer such thatonly patches of GeSi and/or Ge remain on the Si, SOI or SOH substrate.In some cases not all the GeSi and/or Ge need to be removed; onlysufficient material is etched so that the bowing is less. The wafer canalso be planarized with the addition of dielectric, amorphoussemiconductor for example and followed by chemical mechanical polishing.Once it is flat and/or almost flat, high resolution photolithography asthose used in CMOS manufacturing, can be used.

In addition, the islands of GeSi/Si and/or Ge layers can be formed byselective area epitaxial growth where patterns of dielectric such asgrids can be deposited on the Si and/or SOI/SOH wafers such thatepitaxial Ge and/or GeSi, and/or Si are grown on bare Si surfaces andamorphous Ge and/or GeSi and/or Si can be deposited on the dielectriclayer which can be silicon dioxide, silicon nitride, silicon carbide toname a few, and/or no significant deposition occur on the dielectrics.

In some cases, using selective epitaxial growth, the GeSi alloy and/orGe can also be grown within the nano/micro structured holes to partiallyand/or fully fill the holes and/or mushroom over the top surface. TheGeSi and/or Ge can be doped P-I-N to match the doping approximately ofthe layers outside the nano/micro structure holes which can be Si and/orGeSI and/or Ge and/or any combination thereof. See, Montalenti et al,Fully coherent growth of Ge on free-standing Si(001) nanomesas, PHYSICALREVIEW B 89, 014101 (2014) (incorporated herein by reference).

FIG. 7B is a top view of a spherical grid pattern of GeSi and/or Ge onsilicon, according to some embodiments. As in the case of FIG. 7A, thepattern relieves bowing of a GeSi and/or Ge on Si. The dark linesrepresent the etched part and the dotted line represent the edge of thewafer. Different grid spacing, and pie cut angles other than 30 degrees,can be used and different etch trench width can be used to optimizedevice density and tradeoff between grid spacing and bowing tolerance.

FIG. 7C shows three examples of nano/micro structure holes filled orpartially filled with GeSi and/or Ge, according to some embodiments. Theholes 712 can be partially filled, fully filled and overflowing withGeSi and/or Ge on a Si and/or SiGe and/or Ge P-I-N (or N-I-P orP-I-P-I-N) structure and any combination of Si, GeSi, Ge layers. Forexample, the bottom of the hole can be Si, GeSi and/or Ge, the I layercan be Si, GeSi and/or Ge and the top P layer can be Si, GeSi and/or Ge.

In some cases, the region without the nano/microstructured holes can beSi P-I-N and in some cases it can be Si/GeSi/Si P-I-N and in some casesit can be Si/GeSi or Si/GeSi or Si or Ge P-I-N (or N-I-P or P-I-P-I-Nfor MSAPD where P-I-P can be Si and/or GeSi and/or Ge and I-N can be Sifor example). After selective area growth of GeSi and/or Ge, additionalnano/micro structured holes 714 can be etched to further optimize theenhancement of absorption by photon trapping and/or slow waves forexample.

FIG. 8 is a diagram illustrating a monolithically integrated singlesilicon chip that can include single and/or multiple combinations ofdevices, according to some embodiments. Silicon chip 800 can anycombination of the following devices: MSPDs; MSAPDs; vertical cavitysurface emitting lasers (VCSEL) that are either wafer bonded to the chipand/or have a precision cavity for dropping the VCSEL into as in asilicon platform; CMOS/BiCMOS ASICs configured for functions such assignal processing, amplifying, transmission, storage, conditioning,analyzing, and/or configured as laser drivers and/or power amplifiers;holes for thermal removal, ventilation of the chip; thermal barriers;transmission lines; and microwave components such as inductors. TheVCSEL 810, typically made of III-V material can be fluidically assembledon to the monolithic integrated chip with electronics andphotodetectors. With post processing steps, electrodes can be attachedto the VCSEL to connect the VCSEL(s) to the driver electronics. TheVCSEL 810 is positioned in a slot or precision cavity in chip 800. Aheat sink at the bottom of the precision cavity can be magnetic toattract the VCSEL and rapid thermal annealing can be used to attach theVCSEL 810. Post processing such as metallic plating can attach themicrowave transmission lines from the ASIC 808 to the VCSEL 810.

FIGS. 9A and 9B are schematic cross sections of a possible MSPD P-I-Nstructure, according to some embodiments. The device can also be a MSAPDP-I-P-I-N structure where the layers can be Si and/or GeSi and/or Gecompositions and any combinations of Si, GeSi and Ge. The P-I-N layerscan be Si and/or GeSi and/or Ge and/or any combination thereof. CMOSand/or BiCMOS layer(s) can be grown on top of the P-I-N (or N-I-P) withor without additional layers.

The top P⁺ layer can be SI and/or GeSi and/or Ge with a thicknessranging from 0.1 to 0.5 microns with a doping greater than 1×10²⁰ cm⁻³with boron for example. The I intrinsic layer, or the very low doped N⁻(or P⁻) layer can have a thickness ranging from 0.5-3 microns, and insome cases 1.8-2.2 microns, and can have a background doping of lessthan 5×10¹⁵ cm⁻³ and in some cases less than 2×10¹⁵ cm⁻³. The I or N⁻layer can be Ge_(x)Si_(1-x) with x between 0 (and including 0) and lessthan or equal to 1. The bottom N layer can be Si and/or GeSi alloyand/or Ge, with thickness ranging from 0.1 to 0.5 microns with dopinggreater than 2×10¹⁹ cm⁻³ with arsenic and/or phosphor for example. Otherdopants may be used in the periodic table for P and N such as carbon,antimony, to name a few but these are less common and seldom used inCMOS processing. The P-I-N layers can be grown on a silicon substratethat can be either P or N doping, or on a SOI (silicon on insulator)substrate with a device layer of either P or N and/or on a SOH waferwith device layers of either N or P.

Microstructure holes 912 are etched into the P-I-N (or N-I-P, orP-I-P-I-N for MSAPD) structure using both wet anisotropic, isotropicetch and dry etching such as DRIE, ICP (inductive coupled plasma), HAR(high aspect ratio) etching as in Wu et al. A mixture of wet and dryetching can be used with a final wet etch to remove any dry etchingdamage to the Si, GeSi, Ge. Hole dimensions, diameter, diagonal, sides,major and minor semi-axis, can range from 200 nm to 3000 nm and in somecases 400 nm to 2000 nm and in some cases from 500 nm to 1800 nm, andspacing between the micro/nano structures can be periodic, aperiodicand/or any combination or periodic and aperiodic; the spacing can rangefrom 0 nm (touching and/or intersecting) to 5000 nm, and in some cases100 nm to 3000 nm and in some cases 100 nm to 2000 nm and in some cases100 nm to 1500 nm. The spacing in the lateral directions, such as the xand y directions on a plane for example, can be different and/or thesame, can be periodic and/or aperiodic and/or any combination ofperiodic and aperiodic. Other geometries such as hexagonal, the distanceto the nearest neighbor holes can be same or different and can beperiodic and/or aperiodic and/or any combination of periodic andaperiodic. Hole dimension can also be different and/or the same asadjacent holes, hole etch depth can also be different and/or the same,hole depth can range from 0.2 microns to 10 microns. As shown in FIG.9B, the holes 912 can be trapezoidal, and/or can have any number ofslopes of its sidewalls and can be etched within the top P layer,partially into the I layer, through the I layer, partially into thebottom N layer, through the N layer to the silicon dioxide layer of aSOI wafer for example or to an etch stop layer in a bulk siliconsubstrate or SOI or SOH for example. Ohmic contacts 920 can be added asshown, for reverse biasing.

The wavelength range, depending on the percentage of Ge in Si, for 0%can range from 840-960 nm and in some cases 840 nm to 990 nm, and with10% Ge or less in GeSi alloy that is either relaxed or not relaxed, thewavelength can range from 840-990 nm and in some cases 840 nm to 1000 nmfor not relaxed GeSi layer and 840-960 nm for relax, for 20% or less Ge,the wavelength can be extended to 1000 nm and in some cases to 1250 nmfor not relaxed GeSi layer and for 40% or less Ge, the wavelength can beextended to 1310 nm and in some cases to 1400 nm. Depending on theamount of strain, the bandgap narrowing of GeSi alloy can vary over awider or narrower range of wavelengths. Quantum efficiency can be 40% ormore at at least one or more wavelengths in the wavelength range.

Etch stop layer(s) can be included, for example heavily doped P layerwith boron, or carbon and Ge can sometimes be added to compensate forthe strain, or a thin layer of GeSi alloy, silicon dioxide buried layer,and/or nitrogen implant. See e.g., Paneva et al, Nitrogen implantedetch-stop layers in silicon, Microelectronic Engineering 27 (1995)509-512 (incorporated herein by reference). The etch stop layer can begrown on bulk silicon substrate, SOH or SOI wafers. In the case of bulkSi wafer, a via 930 can be etched to remove most or all of the substrateto the etch stop layer which can in addition be patterned withnano-micro structures 914 and/or can be coated with dielectricdistributed Bragg reflectors. By removing most and/or all of thesubstrate beneath the MSPD/MSAPD, provides a semiconductor-air interfaceand allow optical signal to reflect and/or to be confined mostly in theI region allowing more efficient lateral propagation and improvingphoton trapping. The lateral propagation of the optical signal withinthe MSPD/MSAPD can be Bloch modes, slow waves, transverse modes, totalinternal reflection waves, that can increase the interaction distanceand duration of the optical signal with the I layer which contribute thebulk of the photogenerated carriers that are swept out toward the anodeand cathode under an externally applied bias voltage which then resultin an electrical signal in the external circuits that are connected tothe anode and cathode (930).

As shown in FIG. 9B, the MSPD/MSAPD can be monolithically integratedwith silicon electronics such as CMOS and/or BiCMOS ASIC that providesignal processing, amplification, storage, analysis, transmission.Arrays of MSPD/MSAPD can be monolithically integrated with CMOS/BiCMOSelectronics. Such arrays greatly simplify the assembly and packaging ofmultichannel optical receivers.

The optical signal can impinge from either the top or bottom surfacesand can be normal and/or off normal by as much as 45 degrees or more.The fiber input angle can range from 0 (normal) to 50 degrees and/or theMSPD/MSAPD can be tilted by 0 (no tilt) to 50 degrees from the verticalaxis. The launching of the optical signal off normal can improve thetrapping of the optical signal with the MSPD/MSAPD thereby improving theexternal quantum efficiency (QE) and also reducing the reflection backinto the optical fiber which can affect the performance of the opticalsystem.

FIG. 10 is a cross section view of three funnel shaped holes, accordingto some embodiments. Within the about the first 400 nm from the surfacethe holes have a funnel with different sidewall angles of 61 degrees(hole 1016), 68 degrees (hole 1014) and 82 degrees (hole 1012), allmeasured from the horizontal plane. Each of the holes have a cylindricalportion of approximately 2100 nm with a diameter of 500 nm. Thediameters of the top funnel holes are 940 nm at 61 degree slope (hole1016), 820 nm at 68 degree slope (hole 1014) and 610 nm at 82 degreeslope (hole 1012). The period of the holes is 1000 nm in a hexagonallattice. All the material in this example is silicon. The bottom layerof the holes is silicon dioxide of 2000 nm thick on Si substrate. Thediameters, slopes, and three-dimensional shapes can be same for allholes that are in or on the same substrate or can differ between holesin or on the same substrate, for this and other embodiments described inthis patent specification. FIG. 11 is a plot showing a FDTD (FiniteDifference Time Domain) simulation for the optical field in a structureas shown in FIG. 10. The funnel holes are in a hexagonal lattice with aperiod of 1000 nm with a certain sidewall angle. The structure is aP-I-N on SOI with 400 nm P layer, 1200 nm I layer and 1100 nm N layer on2000 nm silicon dioxide on silicon for example (this was the non optimalstructure after epitaxial growth where the dopant diffused as used in anexperimental testing). The plot shows the QE due to enhanced absorptionin the I layer verses incident optical photon wavelength from 800 nm to900 nm. The solid curve 1116 is for a funnel with a slope of 61 degrees,the dash curve 1114 is for a slope of 68 degrees and the dash dot curve1112 is for a slope of 83 degrees. As can be seen from the simulation,the shallow slope funnel of 61 degrees gave the highest QE ofapproximately 60% from 800-900 nm with a slight droop toward the 900 nmwavelength. For this simulation, the material was all silicon, howeverthe general trend holds for other material such as GeSi and Gehomojunctions, single heterojunctions and/or double heterojunctions andfor other wavelength ranges such as 840 nm to 960 nm, 840 nm to 1000 nm,900 nm to 1250 nm, 1250 nm to 1350 nm, 1350 nm to 1450 nm, 1450 nm to1550 nm, 1550 nm to 1650 nm, and any wavelength between the rangesmentioned. QE can be 40% or greater at least for wavelengths in theranges and/or between the ranges.

Experimental results of QE (external quantum efficiency) of 50-60% wereobserved at 800-850 nm wavelength with this structure.

It can be seen that nano/micro structured holes with a wide funnel canbe more efficient at absorbing and trapping photons that a similar holewith a higher sloped funnel and/or no funnel.

FIG. 12A is a plot of a FDTD simulation of a hexagonal lattice withholes given in FIG. 10 where the holes are funnel shaped with a funnelslope of 61 degrees. The vertical axis is QE and the horizontal axis isoptical wavelength from 800-900 nm and the material is silicon on SOI.The solid line (1212) is a P-I-N or N-I-P structure on 2000 nm silicondioxide on silicon substrate where the layer thicknesses are 400 nm forthe top doped P or N layer, 1200 nm not intentionally doped and/orintrinsic I layer, and 1100 nm oppositely doped from the top layer N orP layer on 2000 nm SiO₂ on silicon substrate. QE is between 50 and 60%in the wavelength span of 800-900 nm. Dashed line (1214) is for athinner layer structure of 300 nm doped top layer P or N, 2000 nm Ilayer, 300 nm oppositely doped from the top layer N or P on 2000 nm SiO₂on silicon substrate, the QE is between 60 and 70% in the wavelengthspan of 800-900 nm. Dash dot line (1216) is for a layer structure of 300nm doped top layer of P or N, 2000 nm I layer, 100 nm oppositely dopedfrom the top layer N or P on 2000 nm SiO₂ on silicon substrate, the QEis between 70-80% for wavelength ranges 800-900 nm. To reduce the seriesresistance of the thin top layer, transparent conducting metal oxidesuch as indium tin oxide (ITO) for example, can be used as an additionallayer on top of the top 100 nm layer. The ITO is transparent at theinfrared wavelengths and can range in thicknesses of 20 nm to 300 nm forexample or any thickness that can reduce the sheet resistances to lessthan 200 ohm square and in some cases less than 100 ohms square and insome cases less than 50 ohms square.

FIG. 12B is a plot showing the QE of a MSPD as in curve 1216 of FIG.12A. The MSPD has a P-I-N or N-I-P layer thickness of 100 nm top P or Nlayer, 2000 nm I layer and 300 nm N or P layer on buried oxide (BOX)layer of 2000 nm on silicon substrate. The QE which is equivalent toabsorption in the I layer is between 70-80% in the wavelength range from800-900 nm. The device layer of the SOI can be P or N for either P-I-Nor N-I-P structures. In some cases a pn junction can be formed betweenthe SOI device layer and the bottom layer of a P-I-N or N-I-P MSPD whichmay or may not have an etch stop layer. The pn junction in some casescan help push away photogenerated carriers in the P or N layer away fromthe I layer thereby reducing a diffusion of minority carriers to the Iregion which can cause a slow response due to a “tail” in the impulseresponse of the MSPD.

The same thin structures can also be applied to MSAPD where the P-I-Players are kept thin, of less than 300 nm and in some cases less than orequal to 100 nm.

Thinner P and N layers can result in higher QE and faster response ofthe MSPD/MSAPD. The same can be implemented in MSAPD where theP-I-P-I-N, the top layer P can be thin with an additional transparentmetal oxide layer to reduce the sheet resistance.

Bandwidth of the thinner P and N layers MSPD can be greater than 10 Gb/sand in some cases greater than or equal to 20 Gb/s and in some casesgreater than or equal to 25 Gb/s and in some cases can be greater thanor equal to 30 Gb/s and in some cases greater than or equal to 40 Gb/sand in some cases greater than or equal to 50 Gb/s. With thinner Ilayer, 50 Gb/s, 60 Gb/s, 80 Gb/s, 100 Gb/s can be achieved.

The thin P and N layers can be implemented in P-I-N (or N-I-P) layerstructures such as Si/Ge_(x)Si_(1-x)/Si (P/I/N) double heterostructures,where x can have values from greater than 0 to 1, and in some casesGe_(y)Si_(1-y)/Ge_(x)Si_(1-x)/Si where x and y can have same and/ordifferent values and can range from 0 to 1, and in some casesGe_(y)Si_(1-y)/Ge_(x)Si_(1-x)/Ge_(z)Si_(1-z) where x, y and z can besame and/or different values ranging from 0 to 1. It is desirable inoptimizing QE and speed of response of the MSPD. The absorbing I layercan be cladded by wider bandgap material that can be less absorbing sothat most of the photo generated electrons and holes are generated inthe I region of the MSPD/MSAPD (MSAPD have two I regions, one for theabsorption of light and the other I region for multiplication; themultiplication I region can be silicon and the absorption I region canbe where x can have values from 0 to 1 and in some cases greater than 0to 1).

FIG. 13 is a plot showing the enhanced absorption(1-reflection-transmission) on the vertical axis and wavelength on thehorizontal axis from 800-900 nm for an all silicon structure shown inFIG. 10. The total thickness is 2500 nm on 2000 nm of SiO₂ on a siliconsubstrate. The three plots are for different slope of the funnel, thebest result is for a funnel slope of 61 degrees in this example. Over90% enhanced absorption can be achieved over a wavelength span of800-900 nm. To maximize the absorption in the I layer, it is desirableto have thin P and N layers in the cases where P and N layers can alsoabsorb photons such as all silicon P-I-N MSPD/MSAPD and in some cases GeP-Ge I-Si N, and in some cases GeSi P-GeSi-I-Si N, in cases where atleast one junction is a homojuction for example. Double heterojuctionswhere the P and N have larger bandgaps than the I layer, and where the Pand N are weakly absorbing, can minimize the generation ofphotogenerated electron hole pairs in the P and N regions. In additionthe optical refractive index of larger bandgap material is in generallower than the refractive index of smaller bandgap material, therefor inthe case of a double heterojunction P-I-N where P and N have higherbandgap than the I region can help confine the lateral propagatingwaves, Bloch waves, slow waves, within mostly the I layer, can improvethe absorption of the photons in the I layer which can further enhancethe absorption and increase the quantum efficiency. Examples of doubleheterojunctions are Si P-Ge_(x)Si_(1-x)I-Si N where x can be greaterthan 0 but less than or equal to 1. Other examples are Ge_(x)Si_(1-x)P-Ge_(y)Si_(1-y) I-Ge_(z)Si₁₋z N and where y is greater than x and z andx and z can be the same or different value. X,y,z can have values from 0to 1. In some cases the x and/or y and/or z can be graded where thevalues can vary within each P,I,N region. Grading can further helpconfine lateral photons within mostly the I region such as for a gradedindex optical fiber or optical waveguide.

In dry etching there are many techniques of monitoring etch depth, oneof the method involves optical interference and/or monitoring thechemical species that are in the etch chamber or exhaust usingspectroscopy. See e.g., Collot et al, Dry-etch monitoring of III-Vheterostructures using laser reflectometry and optical emissionspectroscopy, J. Vac. Sci. Techno!. B 9 (5), September/October 1991(incorporated herein by reference). Similarly, in etching Si, GeSi, Gewith P and N dopings optical interference can be used where GeSi/Si canform an optical interference layer, and/or sensing the species of Ge,As, B in the reaction by product during dry etching using a spectrometereither optical and/or mass spectrometer.

Using etch depth monitoring, thin P and N layers can be used in theP-I-N MSPD (also MSAPD for P-I-P-I-N layers), the thin layers of Pand/or N can be fortifiled with transparent conducting metal oxide suchas indium tin oxide and/or metal layers to reduce the sheet resistivity.P and N layers can be as thin as 100 nm or less, and can be Si, and/orGeSi and/or Ge.

FIG. 14 is a cross section schematic of a MSPD monolithically integratedwith CMOS/BiCMOS electronics in a single chip, according to someembodiments. The chip can include multiple MSPD (and/or MSAPD) withsingle and/or multiple CMOS/BiCMOS electronic application specificintegrated circuits. Each such integrated chip can be the opticalreceiver for either unidirectional and/or bidirectional optical fiberusing a single fiber and/or multiple fibers and/or free spaceapplications for optical data communications. On a bulk Si substrate ofeither N or P doping, and/or a SOI substrate where the device layer canbe either N or P doping and/or on a SOH wafer where the device layer canbe either N or P doping, on which an etch stop layer of GeSi and/or Silayer(s) can be grown of thickness ranging from 50 nm to 200 nm or more,followed by a highly doped and/or degenerately doped N Si and/or GeSilayer(s) of thickness ranging from 50 nm to 300 nm or more, followed byan intrinsic I layer that is not intentionally doped and/or lightlydoped with doping level less than 3×10¹⁵ cm⁻³ that is Si and/or GeSilayer(s) with thickness ranging from 500 nm to 5000 nm and in some casesfrom 500 nm to 2000 nm followed by highly doped (5×10¹⁸-10²⁰ cm⁻³ dopantconcentration or higher) and/or degenerately doped (10²¹ cm⁻³ or higherdopant concentration) P Si and/or GeSi layer(s) with thicknesses rangingfrom 30 nm to 300 nm or more, followed by a buffer Si and/or GeSilayer(s) if necessary and followed by Si and/or GeSi layer(s) forCMOS/BiCMOS electronics which can have multiple layers of CMOS/BiCMOSelectronics which are electrically connected to one or more MSPD and/orMSAPD. In the case of MSAPD, P-I-P-I-N layers are used and where eachlayer can be Si and/or GeSi layer(s), and in some cases themultiplication I layer adjacent to the N layer is Si. In all the GeSilayer(s), the fraction of Ge in each layer(s) can be same and/ordifferent, and in some cases it is desirable that the I absorbing layeris cladded by higher bandgap material, for example the cladding P and Nlayers have less Ge and/or no Ge than the I GeSi layer. It should benoted that all layers absorb photons to some extend, but thephotogenerated carriers in the I absorbing layer contribute the most tothe high speed properties of the MSPD and/or MSAPD. Photogeneratedcarriers in the P and N regions can result in minority carrier diffusionback to the high electric field I absorbing region that can result in aslow tail to the fast impulse response of the MSPD/MSAPD that candegrade the speed or bandwidth of the MSPD/MSAPD.

Also shown in FIG. 14 is a via 1430 where the substrate is mostly and/orentirely removed and micro and/or nano structures can be etched or notetched into the bottom layer(s) and further the bottom layer can becoated with a transparent conducting metal oxide such as indium tinoxide and/or semitransparent metal layer and/or metal layer and/ordielectric Bragg reflector layer(s). The Bragg reflector layers can alsobe a bandpass filter for coarse wavelength division multiplexing (CWDM)applications and light can impinge from the bottom and the via can be aguide for the fiber for example. The top layer(s) can be etched withmicro-nano structure holes 1412 using dry and/or wet etching methods andthe depth of the holes can range from 50 nm to 3000 nm or more, and insome cases partially into the I layer, and/or through the I layer and/orpast the I layer as shown in FIG. 14. The holes 1412 can be periodic ina lattice structure and/or non periodic and/or in a random and/or pseudorandom pattern, the holes can have any shape and the shape can vary withdepth into the layer(s), the diameter and/or diagonal and/or a measureof its size, can range in value from 250 nm to 5000 nm and in some casesfrom 350 nm to 2300 nm for wavelength ranges of 800 nm to 1600 nmdepending on the composition of the I absorbing layer(s) which can be Siand/or Ge_(x)Si_(1-x) layer(s) with Ge fraction x ranging from 0 to 1.External quantum efficiency can range from 15% to 90% or more at atleast one of the wavelengths in the range. In some cases for Si Iabsorbing layer the wavelength can range from 800 to 990 nm with thequantum efficiency (or absorption in the I layer) ranging from 20% to90% at some wavelengths in the range. In some cases at 990 nm the QE canbe equal to and/or greater than 20% and in some cases equal to and/orgreater than 40% for a MSPD. Data rate bandwidths can be 10 Gb/s and insome cases 25 Gb/s and in some cases 50 Gb/s and in some cases greaterthan 50 Gb/s.

Layer 1450 is a thin ITO like material, and/or thin metal material withthickness ranging from 5 nm to 500 nm or more that can be deposited onthe P and/or N layer(s) to reduce the sheet resistance of these layers.In some cases with the addition of transparent conductive metal oxideand/or metal layers the P and N layers can be medium doped (10¹⁷-10¹⁸cm⁻³ concentration of dopants) and/or low doped (10¹⁶ cm⁻³ dopantconcentration or less). Ohmic contacts 1420 to the P and N regions aremade and transmission lines 1442 connect the MSPD and/or MSAPD to theCMOS/BiCMOS electronics. A reverse bias is applied between the anode andcathode, the bias voltage can range from −2 to −4V and in some cases −2to −6V for MSPD and −10 to −50V for MSAPD. Light can impinge from thetop surface at a normal and/or almost normal incidence to the surface,and in some cases it can be off normal by an angle ranging from 5degrees to 50 degrees off normal. In some cases, off normal providesless reflection back into the fiber. Reflection can be as low as 5% orless and in some cases 3% or less and in some cases 1% or less from thesurface of the MSPD/MSAPD back into the fiber and/or back toward theincident beam of light. The schematic in FIG. 14 only shows basicfeatures for clarity.

FIG. 15 is a plot of a FDTD simulation of absorption in the I layerwhich is equivalent to the quantum efficiency of a structure similar toFIG. 10. The funnel angle is 61 degrees and 400 nm in depth followed bya cylindrical section of 2200 nm. The MSPD P-I-N structure is 300 nm P,2000 nm I and 300 nm N on SOI where the oxide is 2000 nm thick onsilicon substrate. The vertical axis is QE (or absorption in the I layeronly), and the horizontal axis is wavelength from 800 nm to 990 nm. Thematerial is all silicon. The simulation shows that the QE range fromover 70% to approximately 60% over the wavelength span of 800-980 nm,The funnel diameter is 940 nm and the cylindrical diameter is 500 nm,with a period of 1000 nm in a hexagonal lattice. This is just oneexample of the hole dimensions, other dimensions ranging from 300 nm to3000 nm and spacing between holes ranging from 50 nm to 3000 nm can beother examples.

In some cases, the QE at 980 nm can be 10% or greater, and in some casesthe QE at 980 nm can be 20% or greater, and in some cases the QE at 980nm can be 30% or greater and in some cases the QE can be 40% or greaterat 980 nm and in some cases the QE can be 50% or greater at 980 nm wherethe absorbing I layer is silicon. The lower QE can be due to othereffects such as scattering and losses due to roughness of the hole'ssidewalls. In some cases, smooth side walls of the holes can reducescattering losses and therefor increase the Q of the collectivelyconnected resonant hole structure for enhancement of the absorption. Qvalues can range from 2 to 500 or more for example for themicrostructured holes for the enhancement of absorption. The Q istypically higher when the material absorption coefficient is low, forexample less than 200 cm⁻¹.

Ingham, Future of Short-Reach Optical Interconnects based on MMFTechnologies, OFC 2017 © OSA 2017 (incorporated herein by reference andreferred to herein as “Ingham”); and Sun et al, SWDM PAM4 TransmissionOver Next Generation Wide-Band Multimode Optical Fiber, JOURNAL OFLIGHTWAVE TECHNOLOGY, VOL. 35, NO. 4, Feb. 15, 2017 (incorporated hereinby reference and referred to herein as “Sun”) discuss the use ofwavelengths 850, 880, 910, 940, 980 nm for coarse wavelength divisionmultiplexing and using PAM-4 (pulse amplitude modulation using 4 pulses)for an aggregated data rate of over 200 Gb/s on a single multimodefiber. In such applications the linearity of the MSPD is important andMSPD have shown that the linearity of photocurrent vs input opticalpower is linear to over 10 mW.

Ingham and Sun discuss an application of MSPD in short reach opticaldata links. In some cases the MSPD can be monolithically integrated withCMOS and/or BiCMOS electronics such as transimpedance amplifier forexample, which can greatly reduce the cost of the transceiver. See,e.g., Tekin, Review of Packaging of Optoelectronic, Photonic, and MEMSComponents, IEEE JOURNAL OF SELECTED TOPICS IN QUANTUM ELECTRONICS, VOL.17, NO. 3, MAY/JUNE 2011 (incorporated herein by reference) and Orcuttet al, Monolithic Silicon Photonics at 25 Gb/s, OFC 2016 © OSA (2016)(incorporated herein by reference) where cost of packaging can besignificantly reduced with monolithic integration of components.

FIG. 16 is a plot of a FDTD simulation of a structure similar to that ofthe plot in FIG. 15 but with a thinner top layer of 100 nm rather than300 nm. The MSPD (can also be MSAPD with the addition of charge andmultiplication layers for the situation where gain is 1) P-I-N (can alsobe N-I-P) where all the layers are silicon with the followingthicknesses, P Si 100 nm, I Si 2000 nm and N Si 300 nm on SOI where theburied oxide layer is 2000 nm on a silicon substrate. The thinner top Player allow more photons into the I layer resulting in an improvement inthe QE of the MSPD/MSAPD. The simulation shows response to 990 nm withQE above 60% and in some cases with QE above 20% at 980 nm and in somecases with QE above 30% at 980 nm and in some cases with QE above 40% at980 nm. The lower QE at 980 nm may be due to scattering losses. The Q at980 nm may range from 4 to 100 or more.

A transparent conducting metal oxide such as indium tin oxide can beused on the top layer to reduce the sheet resistivity. The ITO thicknesscan range from 10 nm to 400 nm. See, e.g., Eshaghi et al, Optical andelectrical properties of indium tin oxide (ITO) nanostructured thinfilms deposited on polycarbonate substrates “thickness effect”, Optik125 (2014) 1478-1481 (incorporated herein by reference).

FIG. 17 is a plot of a FDTD simulation of a structure similar thatplotted in FIG. 15 but with P and N layers of 100 nm thick, for a MSPDP-I-N structure as P Si 100 nm, I Si 2000 nm, N Si 100 nm on SOI withoxide thickness of 2000 nm on silicon substrate. As shown in FIG. 14,materials other than SOI may be used, for example, bulk Si where a viais etched and/or on SOH substrate and where the SOH substrate and/or SOIwafer may have different hole pattern and/or photonic crystal and/orhigh contrast grating (HCG) and/or grating filters for each MSPD in anarray for CWDM where light can impinge from the substrate side through avia. With thinner P and N layers more photons are absorbed in the Ilayer resulting in higher QE over the wavelength span from 800-990 nm.The Y axis shows absorption in the I layer which is equivalent to QE andthe X axis is the wavelength in microns. With the thin P and N layers,metal layers, thin semitransparent metal layers, transparent conductingmetal oxide may be used to reduce the sheet resistance. As shown in FIG.14 a via in the backside can be etched to allow the coating of a metalor ITO type material to reduce sheet resistance and other dielectricsfor reflectivity such as Bragg reflectors. The via can also be used as alight guide and/or to guide an optical fiber toward the MSPD/MSAPD.

QE can be as high as over 80% at some wavelengths in the range from800-980 nm, and in some cases over 20% and in some cases over 30% and insome cases over 40% and in some cases over 50% and in some cases over60%.

FIG. 18A-18E are schematic diagrams of microstructured holes positionedon a photosensitive surface of a MSPD/MSAPD, according to someembodiments. In FIG. 18A, the microstructure holes 1812 for enhancingabsorption can be grouped near the center of the MSPD/MSAPDphotosensitive region that can be defined by a mesa 1802 for example.For clarity other components of the MSPD/MSAPD are not shown such as theP or N metal ohmic contacts, electrodes, mesas, passivations, dielecticand/or polyimide, antireflection coatings.

FIG. 18B shows that in addition to the microstructure holes 1812 in thecenter for absorption enhancement, the periphery of the photosensitivearea of a MSPD/MSAPD can have photonic crystal holes 1814 to reflectlaterally propagation optical modes back toward the photon absorbing andabsorption enhancement regions.

FIG. 18C shows microstructured holes 1812 can be in a aperiodic and/ornon periodic arrangements as compared to a periodic arrangement shown inFIGS. 18A and 18B.

FIG. 18D shows that the microstructured holes 1812 can have differentshapes and sizes and can be periodic and/or non periodically arranged.

FIG. 18E shows that the microstructured holes 1812 can cover most of thephotosensitive areas of a MSPD/MSAPD.

The holes in FIGS. 18A-E, can have characteristic dimensions (diameter,diagonal, average dimensions) that range from 100 nm to 3000 nm and insome cases from 250 nm to 2000 nm and in some cases from 500 nm to 1500nm and in some cases from 600 nm to 2500 nm. Spacing between adjacentholes and/or nearest neighbor holes can range from 10 nm to 5000 nm andwhere the holes can be periodic, non periodic, partially periodic,and/or any combination of periodic and/or non periodic and/orrandomness. The diameter or characteristic dimension of thephotosensitive area can range from 5 micrometer to 500 micrometers ormore. In some cases for high speed applications, the diameter of thephotosensitive area can range from 5 micrometers to 100 micrometers andin some cases from 30 micrometers to 80 micrometers.

FIGS. 19A-19D are a series of cross section views illustrating holesbeing etched into a buried oxide layer of a SOI wafer, according to someembodiments. FIG. 19A shows the starting wafer. FIG. 19B shows oxide1904 formed on wafer 1902 and holes 1914 etched in the oxide. In FIG.19C, the wafer and oxide 1902 and 1904 are flipped and bonded to ahandle silicon wafer 1906. In FIG. 19D, the wafer 1902 is cut and/orsubjected to CMP. The pattern of holes 1914 can be a one or twodimensional grating, photonic crystal lattice and/or any other holepatterns that can be used as a filter such that a bandpass region existin the wavelength span. FIGS. 6A-6D show an alternative where the holes632 can be etched directly into silicon. For photons with energiesgreater than the Si bandgap, oxide with holes is less absorbing and forphoton energies less than the Si bandgap, silicon with holes can be usedsince it is minimally absorbing.

These holes 1914 are etched in a pattern to allow a bandpass and areetched at specific locations on the wafer such that MSPD/MSAPD arrayscan be fabricated over the holes either in the oxide and/or in thesilicon such that each MSPD/MSAPD in an array can have a distinctbandpass filter associated with the array or with each or two or moreindividual MSPD/MSAPD in the array. This enables coarse wavelengthdivision multiplexing (CWDM) optical signal to be selectively detectedby the MSPD/MSAPD and/or photodiodes without absorption enhancement holearrays.

Alignment marks can be provided in the oxide and/or silicon such thephotolithographic process using stepper at the device level can align tothe patterns in the SOI with holes and/or SOH substrates.

FIGS. 19E-19H are a series of cross section views illustrating holesetched into the oxide of a SOI wafer that are filled with a high indexdielectric, according to some embodiments. Examples of the high indexdielectric include: hafnium oxide; silicon nitride; zirconium oxide;hafnium nitride; and zirconium. This provides a higher index grating.The holes can be etched partially into the oxide, through the oxide,and/or into the silicon handle substrate. The holes 1916 can bepartially filled, and/or completely filled with another dielectric(s)and/or amorphous semiconductor and can be multiple layers. Surfacenormal color filters can be fabricated in this manner. See, e.g., Uddinet al, Highly efficient color filter array using resonant Si3N4gratings, 20 May 2013| Vol. 21, No. 10| DOI:10.1364/OE.21.012495| OPTICSEXPRESS 12497 (incorporated herein by reference and referred to hereinas “Uddin”); Jacob et al, Normally incident resonant grating reflectionfilters for efficient narrow-band spectral filtering of finite beams,Vol. 18, No. 9/September 2001/J. Opt. Soc. Am. A (incorporated herein byreference); and Zhou et al, Surface-normal emission of a high-Qresonator using a subwavelength high-contrast grating, 27 Oct. 2008/Vol.16, No. 22/OPTICS EXPRESS 17282 (incorporated herein by reference). Thefilter can be photonic crystal, grating and high contrast grating in oneand/or two dimensions that are photo lithographically imaged and wetand/or dry etched in to silicon dioxide, any high dielectric such ashafnium oxide, silicon layer(s) substrate prior to epitaxial depositionof MSPD P-I-N layers and/or MSAPD P-I-P-I-N layers in Si and/or GeSiepitaxial layers.

In some cases photons with wavelengths from 900 nm to 1100 nm can beused with silicon as a photonic crystal, grating and/or high contrastgrating Ref. Zhou. For wavelengths 1000 nm and/or longer, Si can be usedas a grating and/or high contrast grating and/or photonic crystal.

FIG. 19I is a diagram showing a silicon wafer having hole patternsetched for bandpass filtering in locations where MSPDs/MSAPDs are to befabricated, according to some embodiments. Wafer 1950 is a silicon waferthat can be a SOI and/or bulk where holes and/or gratings 1914 (see FIG.19B) are formed in one or two dimensions. The holes and/or gratings 1914are etched in specific locations which match the position 1952 whereMSPDs/MSAPDs are to be fabricated. The MSPSs/MSAPDs can be fabricated onepitaxial layers grown on the substrate with the holes and/or gratings1914 forming a bandpass filter and can select the wavelength in a CWDMor dense wavelength division multiplexing (DWDM) optical signalimpinging on the bandpass filter prior to impinging on the MSPD/MSAPD.This arrangement allows integration of a bandpass filter specific toeach MSPD/MSAPD in an array of two or more MSPD/MSAPD photodetectorsthat are monolithically integrated with CMOS and/or BiCMOS electronicsincluding ASICs such as transimpendance amplifiers for example.

Bandpass filters can also be fabricated on the top surface where themicrostructured holes for absorption enhancement are etched. By using aviscous spin on glass polymer, a glassy film can be deposited over themicrostructured holes without filling the holes. Subsequent siliconnitride or hafnium oxide can be deposited and a grating in one and/ortwo dimension can be etched to form a bandpass filter. See, e.g., Uddin.

FIG. 20 is a cross sectional diagram showing several filters, eachhaving a different passband for each of several MSPDs, according to someembodiments. Note that some or all of the MSPDs can also be MSAPDs. TheMSPDs form an array where each MSPD1, MSPD2, MSPD3, . . . MSPDn has abandpass filter with its own unique bandpass wavelength. Having adifferent bandpass wavelength for each of the MSPD in the array allowsfor the selection of specific wavelengths in a CWDM optical signal. Oneexample is to bounce the incoming CWDM signal 2060 off a reflector 2052and through the first bandpass filter 2014 and into MSPD1 2024. Bandpassfilter 2014 is configured such that only a specific wavelength range istransmitted to MSPD1 2024 and the rest of the CWDM signal 2056 isreflected back toward the reflector 2052 where it is bounced into thesecond MSPD2 2026 and a specific wavelength range is selected fortransmitting through the bandpass filter 2016 toward MSPD2 2026, therest of the CWDM wavelengths 2058 are reflected back toward thereflector 2052 where it then bounce to the next MSPD in the array (MSPD32028, having its own bandpass filter 2018). For light impinging from thebottom though a via, the top surface of each MSPD that includesmicrostructured holes for absorption enhancement can be covered with adielectric such as spin on glass followed by a metal layer to reflectlight that propagates through the P-I-N structure and reflect backtoward the microstructured holes for absorption enhancement.

FIG. 21 is a simple schematic diagram showing MSPD/MSAPD arraysmonolithically integrated with CMOS and/or BiCMOS electronics, accordingto some embodiments. The MSPDs/MSAPDs (MSPD1, MSPD2, MSPD3, MSPD4, etc.)are connected to the CMOS/BiCMOS electronics with a transmission line2142. Directly below the MSPD/MSAPD are the bandpass filtergrating/holes and via (dotted circle 2130) for allowing light to impingeon the bottom surface and/or to act as a light guide for optical fibers.Each MSPD/MSAPD can have a different bandpass filter that allows aspecific wavelength span to be transmitted to the MSPD/MSAPD. Themonolithically integrated chip 2100 can be flipped and the electronicscan be solder bumped to external circuits such as on a printed circuitboard (PCB) (not shown) for electrical signal transmission andelectrical power. The monolithic integration also significantly reducesparasitic capacitance, inductance and resistances and can significantlyimprove the performance of the monolithically integrated opticalreceiver.

FIGS. 22A and 22B are diagrams illustrating cost savings from using amonolithically integrated MSPD(s)/MSAPD(s) with ASIC(s). FIG. 22A showsa conventional packaging arrangement used in short, medium and longreach optical data communication links. FIG. 22B shows a packagingarrangement according to some embodiments of this disclosure wherein anMSPD/MSAPD is monolithically integrated with ASIC(s) which can includeTIA(s), signal processors, storage, transmission electronics, centralprocessing units (CPU), pre amplifiers, amplifiers, etc. into a singlesilicon chip. In both FIGS. 22A and 22B the optical fiber 2250 (e.g MMF)received the optical signal from a VCSEL 2280. The VCSEL 2280 is mountedalong with an LD driver 2282 to a multichip carrier 2270. The carrier2270 in turn is mounted, for example using solder bumps, to a printedcircuit board 2260. In FIG. 22A, the photodiode (PD) 2290 is separatefrom the ASIC 2292 such as TIA (transimpedance amplifier). The PD 2290and TIA 2292 are each bonded to a substrate 2250, which in some cases isa ceramic multichip carrier, in some cases a glass substrate, and insome cases another silicon piece. FIG. 22B shows an arrangementaccording to some embodiments of this disclosure, where for short reach,medium reach and long reach optical data communication, theMSPD(s)/MSAPD(s) are monolithically integrated with ASIC(s) on a singlesilicon substrate 2200 thereby significantly reducing the cost ofpackaging and parts needed, in addition to improving performance of theoptical receiver. See, e.g., Tekin, Review of Packaging ofOptoelectronic, Photonic, and MEMS Components, IEEE JOURNAL OF SELECTEDTOPICS IN QUANTUM ELECTRONICS, VOL. 17, NO. 3, MAY/JUNE 2011(incorporated herein by reference); and Doany et al, 300 Gb/s 24-ChannelBidirectional Si Carrier Transceiver Optochip for Board-LevelInterconnects, 2008 Electronic Components and Technology Conference(incorporated herein by reference) which discusses cases where the PDand TIA are separate chips and need to be attached to a third commonsubstrate.

FIG. 23 is a simple schematic diagram showing MSPDs/MSAPDs in an array,according to some embodiments. Although FIG. 23 illustrates MSPDs/MSAPDs2300 arranged in a two-dimensional array, in some cases they can bearranged in a one-dimensional array, and in some cases they can bearranged in a three-dimensional array. In all cases the MSPD/MSAPD inthe array are monolithically integrated with ASIC(s). The transmissionlines from the MSPD/MSAPD are not shown for simplicity. The array can beused for optical data communication. According to some embodiments, thearray can be used for light distance and ranging (LIDAR) applications,such as for: vehicles, robots, wheel chairs, drones, and/or smart canesfor people with sight impairments. Silicon MSPDs/MSAPDs can be used inwavelength ranges from 780-990 nm, and GeSi MSPD/MSAPD can be used inwavelength ranges 850-1400 nm and longer depending on the Ge fraction inGeSi for the absorbing I layer. The two-dimensional array ofMSPDs/MSAPDs can offer an imaging of the light bouncing back from anobject or objects. See, e.g., Poulton et al,http://spectrum.ieee.org/tech-talk/semiconductors/optoelectronics/mit-lidar-on-a-chip(incorporated herein by reference); and Rasshofer et al, Influences ofweather phenomena on automotive laser radar systems, Adv. Radio Sci., 9,49-60, 2011 (incorporated herein by reference). Conventional Si PDs canreach 3 Gb/s in the near infrared wavelength ranges. For higher datarates, MSPDs/MSAPDs as described herein can be used. According to someembodiments, MSPDs/MSAPDs as described herein can provide data rates of5, 10, 20, 25 Gb/s or more with QE better than 30% at near infraredwavelengths. The QE can be further improved using MSAPD for example.

In some cases, the array can be MSAPDs for LIDAR applications where theI or low doped layer for photon absorption and trapping can be GeSiwhere the Ge fraction can range from 0 to 1. The structure can be aPIPIN avalanche photodiode structure where the avalanche and/or gain cantake place in a Si and/or GeSi I layer, as shown in multiple examples ofMSAPDs throughout this disclosure. The data rate bandwidth can be lessthan a few Gb/s, in some cases less than 10 Gb/s, in some cases lessthan 25 Gb/s and in some cases less than 1 Gb/s. The addition ofmicrostructure holes for photon trapping can reduce the overallthickness of the APD and can result in a reduction of the avalanchevoltage which can be desirable in some applications, such as thoserequiring reliability in hostile environments. The photosensitivediameter or lateral dimension of each MSAPD can range from 100 micronsto 1000 microns or more. In some cases the lateral dimension of thephotosensitive area of a MSAPD in the array can range from 50 microns to5000 microns. The monolithically integrated chip can have a dimensionssuch as: millimeters by millimeters; millimeters by centimeters; andcentimeters by centimeters. The microstructure holes can be fullypassivated to reduce any excess dark current and the MSAPDs can beentirely passivated for reliability. The I low doped layer for photonabsorption and trapping can have a thickness ranging from 2 to 10microns and can be tailored for the data rate bandwidth, responsivity orQE and avalanche voltage.

In some cases, three-dimensional arrays can be made by stackingtwo-dimensional arrays (such as shown in FIG. 23) on top of each otherand where the top arrays are silicon for example and response towavelengths from 700-1000 nm and the middle array can be GeSi respondingto wavelengths from 1150-1350 nm and the bottom array can be Geresponding to wavelengths of 1400-2000 nm for example and where lightimpinge from the top surface and where the shorter wavelengths areabsorbed first and the top array can be transparent to the longerwavelengths and allow it to pass through. This can be used in LIDARand/or CWDM and other applications that may have large wavelengthsspans. In this described example three stacked 2D arrays can beprovided. According to some embodiments, more than 3 may be possiblewith changes of Ge fraction in the GeSi alloy.

In FIGS. 21 and 23 the array of MSPDs/MSAPDs can also include bandpassfilters such that specific wavelengths can be addressed to eachMSPD/MSAPD and is some cases groups of MSPDs/MSAPDs can have specificbandpass filters. By using color filters and single and/or multiplearrays of MSPDs/MSAPDs, single and/or multiple wavelength imaging LIDARcan be provided for further image processing and enhancement for exampleto remove background noise and interference.

In LIDAR applications, the array of microstructured photodetectors(MS-PD) can be microstructured avalanched photodiodes (MSAPD) and wherethe photosensitive area of the MSAPD can be larger than for a high speedMSAPD for data communications. For LIDAR, the diagonal, assume a squarephotosensitive region, can range from 50 to 500 micrometers and thethickness of the I layer where photogenerated carriers are swept out dueto the high electric field, can range from 500 nm to 5000 nm and in somecases from 500 nm to 2000 nm and in some cases from 500 nm to 1200 nm.LIDAR time resolution can range from 100 ps to nanoseconds. MSAPD allowthe layers to be thin and therefore the avalanche voltage can be lower.See e.g., Youn et al, 10-Gb/s 850-nm CMOS OEIC Receiver with a SiliconAvalanche Photodetector, IEEE JOURNAL OF QUANTUM ELECTRONICS, VOL. 48,NO. 2, FEBRUARY 2012 (incorporated herein by reference and referred toherein and “Youn et al”), which shows less than 11V reverse bias andKang et al, Epitaxially-grown Ge/Si avalanche photodiodes for 1.3 μmlight detection, 23 Jun. 2008/Vol. 16, No. 13/OPTICS EXPRESS 9366(incorporated herein by reference and referred there herein as “Kang etal 2008”), which shows an approximately −27V reverse bias. With MSAPDs,the mircrostructure holes allowing photon trapping can have thinnerlayers and therefore lower reverse bias voltage which is desirable insystem applications. Reverse bias voltages in the range −6 to −25 voltsfor MSAPD can be developed and integrated with CMOS/BiCMOS electronicsfor signal and/or image processing. By timing the time of flight forphotons pulses from a vertical cavity surface emitting laser (VCSEL)array at wavelengths that can range from 780 nm to 1350 nm and in somecases 850 nm to 980 nm and the time the MSPD and/or MSAPD receives thesignal, the distance and/or the image such as the shape of the objectreflecting the laser pulses can be determined. For LIDAR applications,sensitivity of the photodetector is important as well as voltage forsystem reliability, and MSPD and/or MSAPD can be used. As will bedescribed infra, microstructure optical waveguide photodiode and/oravalanche photodiode (MSOWPD/MSOWAPD) may also be used for thisapplication.

FIGS. 24 and 25 are schematic cross section views of a MSAPD with holesthat can have various shape, according to some embodiments.Microstructure holes 2412 in general can have any shape, and in somecases are pyramidal, funnel shaped, cylindrical, polygonal, and/or acombination of shapes. Various fabrication techniques can be used aloneor in combination including: wet etching; dry etching; ion milling; andother ways of removing semiconductor and/or non semiconductor material.Starting with a silicon substrate that can have a buried oxide (BOX)layer and/or buried hole layer (SOH silicon on hole), and/or with orwithout an etch stop layer and/or the device layer of the SOI can be Nand/or P on which cathode N layer is grown with doping concentrationranging from 5×10¹⁸ to 2×10²⁰/cm³ and thickness ranging from 50 nm to500 nm; the multiplication Si layer is grown with doping concentrationranging from 1×10¹⁵ to 2×10¹⁶/cm³ and thickness ranging from 200 nm to800 nm and in some cases the multiplication layer can be Ge_(x)Si_(1-x)where the Ge alloy fraction x can range from less than 1% to 10% ormore, followed by a charge layer that can be Si and/or GeSi where the Gealloy fraction can range from less than 1% to 10% or more and is grownwith p-type doping concentration ranging from 8×10¹⁶ to 5×10¹⁷/cm³ andthickness ranging from 50 nm to 200 nm; followed by an I (intrinsicand/or not intentionally doped) high field layer where photons absorbedin this region contribute the bulk of the high speed response of theMSAPD to an optical signal, in some cases also called the absorptionlayer (even though other layers may also absorb photons but have lesscontribution to the high speed response of the MSAPD to an opticalsignal), that can be Si and/or GeSi with the Ge alloy fraction rangingfrom less than 1% to 100% (all Ge) and is grown with dopingconcentration ranging from 5×10¹³ to 6×10¹⁵/cm³ and thickness rangingfrom 500 nm to 5000 nm; followed by the anode P layer which can be Siand/or GeSi where the Ge alloy fraction can range from less than 1% to100% and is grown with doping concentration ranging from 5×10¹⁹ to5×10²⁰/cm³ and thickness ranging from 50 nm to 500 nm and in some cases10 nm to 10000 nm; and in some cases a thin metal such as Ag, Au, Pt,Ni, Cr, Al, Zr, and/or metal alloys and/or silicide such as AlSi, NiSito name a few and/or transparent metal oxide such as indium tin oxideand/or any combination of metal, transparent metal oxide, silicideand/or other conducting transparent semitransparent to the opticalsignal material may be used on the surface of the P anode layer tofurther reduce sheet resistance of the anode layer. Thickness of suchlayers can range from 5 nm to 500 nm.

Holes 2412 can have diameters and/or a significant dimension such as adiagonal, ranging from 100 nm to 5000 nm and in some cases ranging from500 nm to 2500 nm and in some cases ranging from 600 nm to 1500 nm, thehole depth can range from 300 nm to 5000 nm or deeper and in some casescan be partially in the I layer and in some cases to the P charge layerand in some cases partially into the multiplication layer and in somecases to the N cathode layer and in some cases partially into the Ncathode layer and in some case through the N cathode layer. A backsidevia 2430 can be etched to remove the substrate to the oxide layer and/orto the etch stop layer and/or to the N layer which can also be a Si/GeSiBragg layer. A coating of metal, transparent conducting metal oxide, canbe applied to reduce the sheet resistance and in addition a dielectricBragg reflector and/or dielectric 2432 can be applied to further enhanceabsorption by reflecting stray light. In addition the Bragg dielectricstack 2432 can be a bandpass filter to allow only certain wavelengths oflight to pass through for certain applications where wavelengthselective detection is desired such as CWDM and/or bi directional freespace optical communication.

Operational wavelengths for all Si layers can range from 780 nm to 980nm and in some cases from 820 nm to 880 nm and in some cases from 820 nmto 950 nm and in some cases from 840 nm to 980 nm with quantumefficiencies better or equal to 20% and/or with responsivity better orequal to 0.1 A/W (amp per watt). In some cases the quantum efficiencycan be better than and/or equal to 50% at at least one wavelength in thewavelength range of 800 nm to 980 nm.

With the addition of Ge in the I layer to form GeSi alloy, with the Gealloy fraction ranging from a few percent to tens of percent, thewavelength can be extended beyond 1000 nm and in some cases to 1300 nmand in some cases to 1450 nm with high Ge alloy percentages. QE can be50% or better at at least one wavelength in the range 980 nm to 1300 nmand in some cases in the range 980 nm to 1450 nm. In some cases the QEcan be 30% or better in at least one wavelength in the wavelength range980 nm to 1450 nm.

Metal ohmics and metal electrodes are applied to the anode and cathodelayers and a reverse bias voltage ranging from −15 to −45 volts can beapplied to the anode and cathode. Light can impinge from the top surfaceand/or from the bottom surface. Gain bandwidth product of the MSAPD canrange from 10 Gb/s to 100 Gb/s or more and in some cases can range from20 Gb/s to 200 Gb/s or more and in some cases from 100 Gb/s to 300 Gb/sor more.

The MSPD and MSAPD can be thought of as lossy high contrast gratingswith Q ranging from 2 to 1000 as compared to a silicon high contrastgrating operating at wavelengths less than the silicon bandgap, and theQ can be as high as one million. In some cases, the smoothness of theside wall of the microstructured holes may be important to achieve Qgreater than 20 for example to Q of 100 that can increase the effectiveoptical path in the I layer by 40 to 200 times.

In addition, metal nanoparticles and/or III-V quantum dots added to theholes, and/or on the surface of the holes, can further assist in theabsorption of photons. In some cases, a via may not be implemented.

FIG. 25 is similar to FIG. 24 except with the addition of a Braggreflector region at the charge layer of Si/GeSi layers that can be oneor multiple periods to reflect partially and/or entirely optical signalsthat are transmitted through the I layer to further enhance theabsorption. The design of the Bragg layer is well known in prior art andconsist of quarter wavelength thickness layers ranging from 60-90 nm inthickness per layer at near infrared wavelengths. For example one periodBragg reflector at 980 nm wavelength can be approximately 140 nm thick.In some cases a via may not be required.

FIG. 26 is schematic diagram illustrating integration of the MSAPDstructure in FIG. 24 with CMOS and/or BiCMOS electronics, according tosome embodiments. Other possible configurations are also possible andthis is just one example. The MSAPD layers are grown first followed bythe CMOS and/or BiCMOS layer(s) if any. Not shown in FIG. 26, the anodeand cathode of the MSAPD are connected to the electronics circuits andbias circuits of the ASIC CMOS and/or BiCMOS electronics for signalprocessing, equalization, conditioning, amplification and transmission.The integration of the MSAPD can be a single device and/or an array ofMSAPD with a single ASIC and/or an array of ASIC and in some cases, theMSAPD can have bandpass filters for example in the photonic crystalholes in the substrate that can select certain wavelengths of light toconvert to electron hole pairs for high speed detection. In the case ofintegration with CMOS/BiCMOS electronics, the I layer can be low dopedand/or undoped with resistivity in the neighborhood of 1-30 ohm-cm ormore, and thicknesses ranging from 0.5 to 5 micrometers and in somecases 0.5-2 micrometers and in some cases about 1 micrometer. A P wellcan be formed on the top I layer by diffusion and/or ion implantation ofP type ions such as boron to a thickness ranging from 100 nm to 500 nmand in some cases 100 nm to 300 nm with a resistivity in theneighborhood of 0.01 to 0.001 ohm-cm or less. In some cases atransparent conducting metal oxide such as indium tin oxide and/or athin metal layer of less than 5 nm thick such as platinum can be used onthe P doped top surface to reduce the series resistance. CMOS/BiCMOSelectronics can be formed on the top I layer with proper P and N wells,dielectrics and metal interconnects as in Swoboda et al, 11 Gb/sMonolithically Integrated Silicon Optical Receiver for 850 nmWavelength, 006 IEEE International Solid-State Circuits Conference(incorporated herein by reference and referred to herein as “Swoboda”).In some cases a via 2430 may not be implemented.

FIG. 27 is schematic diagram illustrating integration of the MSAPDstructure in FIG. 24 with CMOS and/or BiCMOS electronics, according tosome other embodiments. FIG. 27 is similar to FIG. 24 except only the Ilayer is GeSi or Si and all other layers are Si. In the case of GeSi Ilayer, the P is doped by diffusion and/or ion implantation into the Ilayer as in FIG. 26, the N layer can be Si and is less absorbing toincident photons for example in the 950-980 nm range and the GeSi Ilayer can be more absorbing. Such double heterojunction is conducive toimproving the QE of the MSAPD (MSPD) and can reduce the diffusion ofphotogenerated carriers in the P and N region which can result in aslower response time for the MSAPD/MSPD. Doping and thickness ranges aresimilar to those in FIG. 24 except for the surface P doped region intothe I layer. An example of integration of the MSAPD with CMOS and/orBiCMOS electronics can be seen showing only the basic layers. CMOSand/or BiCMOS layers and/or P and N wells can be formed directly on theI layer and/or can be grown on top of the I layer. The CMOS and/orBiCMOS electronics can be fabricated first together with any concurrentor similar steps such as diffusion and/or doping for the MSAPD/MSPS.This can be followed by forming the MSAPD (MSPD) microstructure holesand the anode and cathode of the MSAPD connected by a transmission lineto the electronics and biasing circuits. Reverse bias voltage can rangefrom −6 to −26 volts. Optical signal can impinge either from the top orbottom surface. Metal, transparent conducting metal oxides can be usedon the P and N surfaces to reduce sheet resistance. In addition metaland/or dielectric mirrors such as Bragg reflectors can be used on thebottom surface after a via to further enhance the QE of the MSAPD/MSPD.Only the very basic elements are shown for simplicity, passivation,planarization, and many other processing steps and elements are notshown. In some cases, via 2430 may not be implemented.

FIG. 28 is a table showing experimental measurements of a MSPD withapproximately 1000 nm thick I layer, 200 nm N layer and approximately1500 nm P layer on 2000 nm BOX on silicon substrate, according to someembodiments. The funnel hole structure and spacing is similar to thoseshown in FIG. 10. The responsivity range from 0.4 NW to 0.1 A/W in thewavelength range from 800 nm to 1000 nm. In the KOH only etched holes,the holes are rectangular inverted pyramids. The MSPD have over 10×higher responsivity than a similar photodiode without microstructures toenhance the absorption and therefore the quantum efficiency.

FIG. 29 is a schematic drawing of a vertical cavity surface emittinglaser (VCSEL) being used together with a MSPD/MSAPD that ismonolithically integrated with ASIC CMOS and/or BiCMOS electronics forclose proximity free space optical data link, according to someembodiments. Device A 2910 includes an optical transmitter 2912 atwavelength 1 and an optical receiver 2914 at wavelength 2. Device B 2920includes an optical transmitter 2922 and an optical receiver 2924. Thetwo devices 2910 and 2920 can transfer data to each other using the twowavelengths 1 and 2 as shown. The close proximity free space (i.e. nooptical cable) link can be used for example with: mobile devices such astablets, laptops, and smartphones; home entertainment boxes; homesecurity boxes; secure payment at stores; and devices to secure banktransactions. Since the laser light can diverge quickly over shortdistances, for example less than one meter and in some cases less than10 centimeters, and in some cases less than 2 centimeters, thecommunication between devices can be very secure and not picked up byunintended recipients. An example of the close proximity optical link isshown, where the transmitter and receiver can be paired with a certainwavelength in one direction and another wavelength in the oppositedirection to minimize cross talk. According to some embodiments, eachmobile device can have multiple ports such that it can multitask severaltransfers of data simultaneously from multiple devices. Data rates canrange from 1 Gb/s to 25 Gb/s or more and in some cases can range from 6Gb/s to 30 Gb/s or more.

Safety features can include low power pinging to see if a recipientreceiver is nearby in close proximity before increasing the laser powerfor high data rate low error transfers.

Other applications can include blade-to-blade free space opticalcommunication in close proximity with multiple high-speed ports at 25Gb/s and greater and in some cases at 50 Gb/s or greater. The opticaltransceiver ports can be located on any surface of the blade or mobiledevice and/or can be attached to an umbilical cord that can bemagnetically coupled to another transceiver to complete the optical datalink. Arrays of optical ports can be implemented on blades and/or mobileand non mobile devices to increase the aggregated data rates to greaterthan 40 Gb/s and in some cases greater than 100 Gb/s and in some casesgreater than 1 Tb/s. Multiple wavelengths can be used in such arrays toavoid cross talks; wavelengths such as 780, 800, 820, 840, 860, 880,900, 920, 940, 960, 980, 1000 nm for example and any other wavelengthsin between and beyond the ranges given.

In some cases, RF and microwave frequencies can be used for proximitydata transmission. In many prior art proximity RF data links, the RFfield is propagating and can be detected by unintended recipientsthereby compromising security. Instead of propagating RF or microwavefields, evanescent RF and/or microwave field should be used such thatthe field is not propagating and can only be transmitted by a closeproximity receiver that can couple the evanescent field to the receiver.An example of evanescent RF/microwave field is the use of metamaterialsuch a RF/microwave superlens where the RF/microwave after the superlensis a near field or evanescent field and decays rapidly over a wavelengthdistance approximately and can couple to another superlens that is inclose proximity of about one wavelength distance and can be detected.Other elements may be also used to detect the evanescent wave such as amicrowave coupler.

FIG. 30 is a cross section view of a basic epitaxial layer structure formonolithic integration of a MSPD with ASICs such as a TIA, according tosome embodiments. The layers can be grown on a silicon substrate N or Ptype, and/or a SOI (silicon on insulator) with a buried oxide (BOX)layer and/or with an etch stop layer and/or with buried holes. If SOI isused, the device layer can be P or N with any resistivity and with alayer thickness ranging from 0.05-0.3 micrometers (micron, um). An Nlayer (N and P can be interchanged, PIN can also be NIP for differentapplications and/or fabrication requirements) of Si and/or GeSi wherethe Ge fraction can range from 0.001 to 0.6 has a thickness ranging from0.05-0.5 microns and in some cases 0.05 to 0.3 microns (micrometers) andin some cases 0.1 to 0.2 microns, and a doping (xEy is the same as x10^(y) dopants/cm³) of greater than 3E19 and in some cases greater than6E19 ora resistivity in the range of 0.005 to 0.001 ohm-cm or less. An ISi and/or GeSi layer where the Ge fraction can range from 0.001 to 1,has a thickness ranging from 0.5 to 5 microns and in some cases 0.5 to 2micrometers and in some cases approximately 1 micrometer. Doping of theI layer is less than 2E15 and/or a resistivity in the neighborhood of1-30 ohm-cm or greater. The I layer may not be intentionally doped andcan have very low P or N doping. In some cases ion implantation duringthe CMOS integration process and/or diffusion process can form a P⁺region on the surface of the I layer with resistivity in theneighborhood of 0.01-0.001 ohm-cm or less and with a thickness rangingfrom 50 nm to 500 nm and in some cases 50 nm to 300 nm and in some cases200 nm. In addition, a Schottky contact and/or ohmic contact with semitransparent metal such as Pt, Al, Cu, Au, Ni, of 50 nm or less thicknessand in some cases 10 nm or less, and/or transparent conducting metaloxide such as indium tin oxide (ITO) can be used to further reduce thesheet reisitance of the P⁺ layer which can have microstructured holes.In some cases a very thin P layer of 0.05 microns or less can be usedand fortified with ITO to reduce the sheet resistance.

CMOS and/or BiCMOS layer(s) in some cases may be grown on the I layerand if it is not compatible with MSPD/MSAPD processing, the layer(s) canbe selectively etched off prior to MSPD/MSAPD processing.

According to some embodiments, many variations to the structure shown inFIG. 30 are possible such as addition of buffer layers, low temperatureGe layers, polysilicon layers, other heterogeneous layers such as GaP,InP, GaAs, InN, GaN, AlN, and AlP.

FIG. 31 is a cross section view showing some aspects of a MSPDintegrated with CMOS/BiCMOS ASICs, according to some embodiments. TheCMOS/BiCMOS ASICs can include one or more of the following: TIAs; clockdata recovery (CDR) circuitry; equalizers; and limiting amplifiers (LA),as some examples. Additional epitaxial layers can be used for theintegration of the ASICs can be formed directly on the I layer with Pand N wells as discussed in Swoboda. The CMOS and/or BiCMOS ASICs can befirst fabricated and some of the steps such as diffusion, ionimplantation, and thermal annealing can be grouped together for the MSPD(or MSAPD) processing steps. Ion implantation can be applied to both theASICs and the MSPD if needed and can be activated together for example.In general, the ASICs can be first fabricated, with some processingsteps that can be shared with the MSPD/MSAPD, followed by MSPDmicrostructure hole etching, wet and/or dry, mesa etching if needed tothe cathode N layer and passivation. Anode and cathode ohmics andtransmission lines connecting the MSPD to the TIA can be formed after anair bridging, if needed, and/or other insulating step where thetransmission lines do not add to extra parasitic capacitance and/orresistances and/or inductances. Mesa diameters can range from 10 to 1000microns, and in some cases from 20 to 80 microns. Other form of definingthe photosensitive area can be disordering of the semiconductor, pnjunction isolation, selective P and N junctions on the surface of the Ilayer, for example. However mesa can have the lowest fringingcapacitance. Passivation to the mesa and microstructure holes can beapplied to reduce surface recombination.

The P surface well, for the P-I-N photodetector can be formed bydiffusion and/or by ion implantation of P type ions such as boron forexample, to a thickness ranging from 50 nm to 500 nm and in some cases50 nm to 300 nm with a resistivity ranging from 0.01 to 0.001 ohm-cm orless, and in some cases semitransparent metal film such as Pt, Ag, Au,Cu, Ni, or V can be deposited on the surface of the P shallow well priorto hole etch. Thickness of the metal can range from 1 nm to 50 nm. Insome cases transparent conducting metal oxide can be used such as indiumtin oxide.

The diameter or diagonal of holes 3112 can range from 200 to 3000 nm andin some cases from 400 to 2500 nm and in some cases from 600 to 1800 nm.Holes 3112 can have same and/or different diameters. Spacing of theholes can range from 10 to 5000 nm and in some cases 10 to 2000 nm andin some cases 10 to 1000 nm and in some cases at least one point of thehole touches the adjacent hole. Holes 3112 can be periodic or aperiodic.The pattern can be periodic in groups of holes while being aperiodicwithin the group. Holes 3112 can be shaped as a funnel, invertedpyramid, cylindrical, hourglass, rectangular, polygonal, amoebic, and/orother shapes. The sidewalls can be smooth and/or textured. The holes3112 can be etched to a depth ranging from 0.2 to 5 microns, and in somecases partially into the I layer and in some cases through the I layerand in some cases to and/or into the N (orP) layer and in some casesthrough the N (or) layer.

Transparent and/or semi transparent metal and/or transparent conductingmetal oxide 3150, such as ITO can be used on the P and N layer to reducethe sheet resistance as shown in FIG. 31.

A via 3130 can be etched through the substrate to the BOX and/or etchstop layer and/or to the N cathode layer such that a metal and/or ITOand/or dielectric layer(s) 3132 can be deposited to reduce the sheetresistance and/or to reflect optical signal back toward themicrostructure region for further absorption enhancements. The bottom Nlayer can be textured and/or with microstructure holes.

Tavernier et al, Power Efficient 4.5 Gbit/s Optical Receiver in 130 nmCMOS with Integrated Photodiode; Solid-State Circuits Conference, 2008.ESSCIRC 2008. 34th European (incorporated herein by reference andreferred to herein as “Tavernier 2008”) discusses a silicon photodiodeintegrated with CMOS electronics. The stand alone silicon photodiode hasreported bandwidth of 500 MHz and responsivity of 5 mA/W at 850 nm. Withintegration to a TIA, the bandwidth improved to 4.5 Gb/s andresponsivity improved to 74 mA/W. Monolithic integration cansignificantly improve the performance of a stand alone MSPD or MSAPD.

CMOS Manufacturing Process, EE141 UCBerkeley,http://bwrcs.eecs.berkeley.edu/Classes/icdesign/ee141_s02/Lectures/Lecture5-Manufacturing.pdf(incorporated herein by reference) discusses basic processes for CMOSprocess which are compatible with MSPD/MSAPD processes.

Data rates can range from 3 to 100 Gb/s or more; operating wavelengthrange for all silicon layers can range from 800-1000 nm withresponsivity greater than or equal to 100 mA/W and in some cases greaterthan or equal to 300 mA/W and in some cases greater than or equal to 600mA/W and in some cases greater than or equal to 800 mA/W for at leastone wavelength in the range.

With a GeSi I layer and with Ge fraction ranging from 0.01 to 1, thewavelength can range from 800-1600 nm and in some cases from 900 to 1100nm and in some cases from 950-1350 nm and in some cases from 990 to 1350nm and in some cases from 990 to 1100 nm and in some cases from1250-1550 nm and in some cases from 1250 to 1450 nm. The responsivitycan be greater than or equal to 100 mA/W and in some cases greater thanor equal to 300 mA/W and in some cases greater than or equal to 600 mA/Wand in some cases greater than or equal to 800 mA/W for at least onewavelength in the range.

A reverse bias voltage ranging from −2 to −10 Volts or more and in comecases −1 to −4V and in some cases −3.3V can be applied to the anode andcathode of the MSPD or MSAPD.

Light shields can be added on top of the TIA/ASICs so that stray lightdoes not interfere with the CMOS operation. The light shield can be alow dielectric constant polymer, black paint, and/or any other materialto block the light illuminating the CMOS ASICs. The light shield can beon the front and/or on the back of the substrate. The backside via isoptional and is used if optical signals impinge from the backside. Insome cases the via can be etched to the BOX layer.

FIG. 32 is a diagram showing a monolithically integrated MSPD with TIAand other ASICs that is flip chip mounted on a printed circuit boardusing solder bump technology, according to some embodiments. The MSPDhas microstructure holes 3212. The via 3230 can be also used to guide amulti mode and/or single mode optical fiber 3260 to the MSPD thussimplifying significantly the optical alignment process. The via 3230can also be at an angle off normal such that the fiber can have an angleoff normal to reduce back reflected optical signal back into the opticalfiber. Anti reflection coating 3232 can be applied to the back Sisurface to further reduce reflection.

In some cases, the optical signal can impinge from the top surface(lower in FIG. 32), and the monolithically integrated chip can be solderbumped to the printed circuit board using through silicon vias (TSV) toconnect the solder bump pads on the bottom surface with the electrodepads on the front surface for example.

FIG. 33 is a diagram showing a similar structure to FIG. 30 but withselective P layer growth, diffusion and/or ion implantation on parts ofthe I layer surface, according to some embodiments. The P layer can havea different bandgap material than that of the I layer. The CMOS/BiCMOSlayer(s) can be selective area growth on the I layer if needed and canbe P and/or N type. The P layer for the PIN MSPD can be formed with ionimplantation process for example, using P type dopants such as B, C, Al,Ga, and/or In. A thermal anneal step is used to activate the dopantsimplanted and/or the P layer can be selective area grown with the sameand/or different bandgap as the I layer. The substrate can be silicon por n type with or without etch stop layers and/or SOI.

FIG. 34 is a cross section view showing some aspects of a MSPDintegrated with TIA/ASICs using a layer structure as in FIG. 33,according to some embodiments. The P layer adjacent to the I layer canbe ion implanted and/or selective area grown. Metal film and/or ITO 3450can be applied as in FIG. 31 to reduce the sheet resistances. Not shownas in FIG. 31 are the transmission lines from the MSPD to the TIA/ASICs.Other features are similar to FIG. 31 including optional via 3430 andmetal, ITO and/or dielectric layer(s) 3432.

In addition, in all the MSPD/MSAPD monolithic integration with CMOS ICs,a light shield 3452 can be added over the CMOS TIA/ASICs such that straylight from the optical signal is kept from impinging on the CMOStransistors, capacitors, which can degrade performance and cause errors.A light shield 3434 can also be added on the bottom of the substrate forbottom illuminated MSPD, MSAPD and/or the light shield can be added onboth surfaces, top and bottom. The light shield(s) can be an opaque (tothe wavelengths of the optical signal and other light sources) polymer,black form, metal, a combination of dielectric and metal, or othermaterials that are mostly opaque to near infrared radiation and/orvisible radiation.

If the optical signal is impinging on the top surface where themicrostructured holes 3412 are, a via 3430 may not be provided, and insome cases the substrate can be a N or P Si substrate instead of a SOIsubstrate. In the case of a N substrate, the cathode can also be on thebottom of the N substrate for example.

FIG. 35 is a cross section view showing an epitaxial layer structure foran MSAPD monolithically integrated with CMOS/BiCMOS ASICs, according tosome embodiments. The structure is similar to that of FIG. 30 with theaddition of a charge and multiplication layers. The charge P layer canbe Si and/or GeSi with Ge fraction ranging from 0.001 to 0.6 or higherand thickness ranging from 0.05 to 0.25 microns and in some cases from0.1 to 0.3 microns and doping ranging from 8E16 to 3E17 and is betweenthe absorption I layer and the multiplication I layer. Themultiplication I layer on top of the cathode N layer can be Si and/orGeSi with Ge fraction ranging from 0.001 to 0.6 and thickness rangingfrom 0.3 to 1.0 microns and in some cases from 0 to 0.5 microns anddoping can range from 1E15 to 1E16 or less or a resistivity of 1-10ohm-cm or higher. The N layer can have a thickness ranging from 0.2 to0.5 microns or more, and a resistivity ranging from 0.01 to 0.001 ohm-cmor lower. In some cases a BOX layer may not be provided and a N typesilicon substrate may be used.

Similarly to FIG. 33, the P top layer can be formed by selective ionimplantation of dopants such as B, Al, C, Ga, and/or In. Any additionalCMOS/BiCMOS layer(s) may be included on the I layer and in some cases,the CMOS/BiCMOS P and N wells can extend into the I layer as discussedin Swoboda. In some cases, the MSAPD process can incorporate anyCMOS/BiCMOS layer by either diffusion doping and/or ion implantation andforming a shallow P well. The CMOS/BiCMOS layers can be selectivelyetched off areas where the MSAPD will be formed. As in FIG. 30 thesubstrate can be silicon N or P type with or without an etch stop layer,or SOI with p or n device layer.

FIG. 36 is a cross section view showing some aspects of a MSAPDmonolithically integrated with CMOS/BiCMOS TIA/ASICs, according to someembodiments. Features shown in FIGS. 31 and 32 can be applied to thisstructure including optional via 3630, optional ITO/metal/dielectriccoating 3650, and optional light shields 3652 and 3634. With a reversebias applied between the anode and cathode of the MSAPD with voltagesranging from −8 to −25 volts, the gain can range from greater than 1 to10 or more, in some cases the gain can range from 2 to 4 and in somecases the gain can range from 2 to 8 or more. Gain bandwidth product canrange from 20 to 300 Gb/s or more. Gain the quantum efficiency can be50% or greater and in some cases 80% or greater and in some cases 100%or greater and in some cases 200% or greater. Responsivity can be 0.5A/W (amperes/watt) or greater and in some cases 1 A/W or greater forsome wavelengths in the range 800-1600 nm depending on the Ge fractionin the GeSi alloy which can range from 0 (all Si) to 1 (all Ge). Ashallow P⁺ well is formed on the surface of the I layer by diffusion ofP type dopants and/or by ion implantation of P type ions. The P⁺ wellcompletes the P-I-P-I-N MSAPD structure, and can have a thicknessranging from 50 to 500 nm and in some cases 100 nm to 300 nm and canhave a resistivity in the neighborhood of 0.01 to 0.001 ohm-cm or lower,In addition, a thin semitransparent metal layer with thickness rangingfrom 1-50 nm and/or transparent conducting metal oxide (TCMO) such asITO with thickness ranging from 1 nm to 500 nm can be deposited on the Pshallow well prior to microstructure hole etch. The addition of metaland/or TOMO can assist in reducing the series sheet resistance of the P⁺shallow well. In some cases, it is desirable to have thin P⁺ shallowwells to reduce the generation of photocarriers in the P⁺ well that canreduce the overall quantum efficiency and/or reduce the data ratebandwidth of the MSAPD due to photogenerated carriers in the P⁺ regiondiffusing to the high field region in the I layer that can result in aslow “tail” in the impulse response. The wavelength range is similar tothe device in FIG. 31. Light shield 3652 can be added to protect theCMOS electronics from stray lights, stray optical signals. The I layerGeSi can have Ge fraction ranging from 0 to 1 (Ge_(x)Si_(1-x) where xcan range from 0 to 1)

In FIG. 1 of Kang et al 2008, a Ge on Si avalanche photodiode is shown.A similar structure can be fabricated with microstructured holes 3612and where the holes can be etched through the contact layer and into theabsorption layer partially and/or entirely. In some cases the holes canbe etched to the charge layer and in some cases through themultiplication layer and in some cases to the bottom contact layer. Asin Kang et al 2008, passivation can be amorphous silicon (a-Si) and/orsilicon nitride.

FIG. 37 is a top view showing some aspects of a MSPD/MSAPDmonolithically integrated with a TIA/ASICs without the solder bumpsand/or bond pads, according to some embodiments. The integrated chip3700 shown can be for a single MSPD/MSAPD 3710 or an array ofMSPDs/MSAPDs. The TIA/ASICs 3702 can also have an opaque coating and/orcover 3752 such that any stray light does not impinge on the CMOS thatcan interfere with the CMOS operation. Light absorbed in the CMOStransistors can generate undesirable electron hole pairs that can changeits operating parameters and can cause errors.

The coating 3752 can be an opaque form like material with low dielectricconstant such that is does not load the CMOS. The opaque material cancover the top surface of the TIA/ASIC 3702 for a top illuminatedMSPD/MSAPD 3710 and/or the bottom surface of the TIA/ASIC 3702 forbottom illuminated MSPD/MSAPD 3710. For a bottom surface coating (suchas coatings 3434 and 3634 in FIGS. 34 and 36), it can be an opaquepolymer for example such as black paint.

Basic fabrication steps can include: CMOS TIA/ASIC steps; etchingmicrostructure holes; forming P ohmic; mesa etch; forming N ohmic; andforming transmission line connecting MSPD/MSAPD anode and cathode to theTIA/ASICs. In some cases, passivation can be inserted before ohmic metaldeposition. For example, such passivation can include: oxidation;deposition of aluminum oxide on the side walls using atomic layerdeposition; depositing poly silicon and/or a-Si; and depositingdielectrics such as hafnium oxide, silicon dioxide silicon nitride andother dielectrics using atomic layer deposition.

Data rates can range from 3 to 100 Gb/s or more for the integrated chipconsisting of MSAPD/MSPD and TIA and other signal processing andenhancing ASICs, and each MSPD/MSAPD can detect the same wavelengthand/or different wavelength with the addition of a bandpass filter thatcan be deposited on the MSPD/MSAPD in the form of dielectric starts suchas Bragg filters for example. Detection at different wavelengths canavoid cross talk.

The MSAPD/MSPD 3710 can have a photosensitive area that can be circular,square, polygonal and can have a diameter and/or diagonal ranging from20 microns to 1000 microns and in some cases for high data rateapplications from 20 microns to 100 microns and for LIDAR applicationsfrom 100 microns to 1000 microns. The distance of the MSAPD/MSPD 3710 tothe CMOS/BiCMOS electronics ICs 3702 can range from a few microns to1000 microns and in some cases from 10 to 250 microns. The first innerring can be the anode 3720 and the outer ring can be the cathode 3722for a P-I-P-I-N MSAPD or a P-I-N MSPD structure.

FIG. 38 is cross section view showing some aspects of a MSPD/MSAPDmonolithically integrated with a TIA/ASICs, according to someembodiments. The structure is similar to that of FIGS. 31 and 34,including microstructure holes 3812, optional via 3830, optionalITO/metal/dielectric coating 3850, and optional light shields 3852 and3634. In FIG. 38, however, a bottom ion implantation process 3880 isprovided, which can either be a blanket ion implantation into the entirebottom surface of the wafer and/or masked such that only certain areasreceive the ions from ion implantation. The ion implantation process3880 can be N type ions such as C, N, P, As, Sb, and/or Bi, implantedinto the N layer (or P type ions can be implanted in P layer, ions suchas C, B, Al, Ga, and/or In) to further increase the doping concentrationthat can reduce the sheet resistance and the minority carrier lifetime.A thermal anneal can activate the implanted ions and remove some of thedamage caused by ion implantation. See, e.g., Williams, Ion Implantationof Semiconductors, Materials Science and Engineering A253 (1998) 8-15(incorporated herein by reference).

In some cases, ions such as Ar, N, O, He, H, and/or Xe can be used tocause damage to the semiconductor in the N or P layer which can furtherreduce minority carrier lifetime. In addition, in some cases, buried ornot buried silicon oxide, silicon nitride layers can be formed with Oand/or N ions implanted into the silicon.

According to some embodiments, ion implantation can also be performedwith or without a conducting layer such as a metal and/or silicode layerwhere the ions can penetrate the metal and/or silicode layer and intothe silicon layer and can be followed by a rapid thermal anneal.

The optical signal can impinge from the top surface and/or from thebottom surface as in FIG. 32. If light is impinging from the bottomsurface, the top surface can include a reflector such that light notabsorbed can be reflected back toward the absorption enhancingmicrostructures.

FIG. 39 is a cross section view an epitaxial layer structure, accordingto some embodiments. The epitaxial layers are grown on a N or P waferand where the layers can consist of an intrinsic I Si and/or GeSI layerwhere the background doping of N or P type is less than 2×10¹⁵/cm³(<2E15) and can have a thickness ranging from 500 nm to 2500 nm and insome cases 500 nm to 3500 nm or more. CMOS layer(s) for TIA/ASICs andother electronics can be grown on the I layer. Not shown are etch stoplayers that can be grown prior to the I layer, marker layer(s) which cancontain a signature ion that can be inactive and/or active, used for dryetching and the etch is monitored by a mass spectroscopy where when thesignature ions are detected, it is know that etching has reached thatlayer. Other etch depth monitoring techniques include the use of opticalinterference, and can include one or more different optical refractiveindex layers to monitor etch depth. Other etch depth monitoringtechniques such as electro chemical etching, resistance monitoring, mayalso be used.

Buffer layers, superlattice layers such as Si/GeSi/Si/GeSi for etchdepth monitoring, lattice matching, bandgap grading, carrier lifetimereduction, isolation, PN junctions, stress reduction and/or enhancementare not shown but can be included between the Si substrate and/or the Ilayer and/or between the I layer and/or the CMOS layer(s) and in somecase can be embedded in the I layer at any location.

The Ge fraction of the GeSi in the I layer can have single and/ormultiple values, and can range from less than 1% to 100%,(Ge_(x)Si_(1-x) where x can range from <0.01 to 1). In some cases Gefraction range from 1% to 10% and in some cases range from 8% to 20% andin some cases range from 20% to 40% or more and the GeSi layer can berelaxed and/or not relaxed.

FIG. 40 is a cross section view illustrating some aspects of MSPD-ASICmonolithic integration, according to some embodiments. The CMOSelectronics can fully or partially fabricated first. In the cases wherethere are common processing steps between the electronics and the MSPD,the steps can be grouped together if possible. For example, in the casewhere the fabrication processes for the CMOS electronics and the MPSDboth call for ion implantation of N and/or P type dopants, the rapidthermal anneal process to activate the implanted ions can be processedtogether for the CMOS electronics and the MSPD. Other examples ofprocesses that can be grouped together are the ohmic contact anneals forthe CMOS electronics and the MSPD.

In FIG. 40, after TIA/ASICs are mostly formed, P type ions using B forexample, can be implanted into the CMOS layer and/or the CMOS layer canbe first partially and/or entirely removed to expose the I layer, and Ptype ions can be implanted into the partial CMOS and/or I layer. P typeions can include B, C, Al, Ga, In for example. A P type region 4084 canbe created with doping ranging from 5×10¹⁹/cm³ to 2×10²⁰/cm³ or higher(5E19 to 2E20 or higher) and an implant range from 50 to 250 nm. See,e.g., Table III of Gibbons, Ion Implantation in Semiconductors-Part IRange Distribution Theory and Experiments, PROCEEDINGS OF THE IEEE, VOL.56. NO. 3, M29 A5RCH 1968 (incorporated herein by reference and referredto herein as “Gibbons”) which gives the P and N type ions and ionimplant energies in to Si with peak position of the ions in Si R_(p) andthe width of the distribution AR_(p). For example, a multiple staggeredimplant with energies of 10, 20, 40, 60, 80, 100 KeV can be used toreach a peak depth of 328 nm of B ions and/or a single implant of 100KeV. The doping is approximately given by dose (ions/cm²)/ΔR_(p) so thatto reach 2E20 at 328 nm depth the dose is approximately 1.5×10¹⁵ions/cm².

A via 4030 is etched in the backside of the Si N (can be P if N and Pare interchanged) type substrate to the I layer and/or almost to the Ilayer and/or to the etch sop/monitoring layers, and/or to the superlattice and ion implant of N type ions such as N, P, As, Sb as given inTable III of Gibbons, can be implanted to create an N type region 4082with doping ranging from 3×10¹⁹/cm³ to 2×10²⁰/cm³ or higher (3E19 to2E20 or higher) and with a thickness of implanted ion range of 225 nm at180 KeV using P ions. Multiple energies can be used to create a smootherdistribution of ions in the N region. Dose of approximately 1E15 can beused to reach a doping of approximately 2E20 with 180 KeV P ions in Si.A rapid thermal anneal can be performed to activate the implanted ions.

According to some embodiments, the P and N regions 4084 and 4082 canalso be formed by diffusion. In such cases, dopants of P and/or N typecan be diffused into Si thermally from either a solid source that can bedeposited on Si surface and/or in close proximity and/or from a gaseoussource.

In addition, Schottky (metal-semiconductor) type junction(s) can beformed at least on either the top and/or bottom Si surface replacing oneor both P to I junction and/or N to I junction in the MSPD/MSAPD. Inaddition to integration, the implant process can also be used for MSPDsingle and/or array photodiodes.

Ion implantation processes can also be used for isolation, where ionssuch as H, O, and/or N can be used and where in some cases O and/or Nions can be implanted to form oxides and/or nitrides of silicon. Thismethod of isolation can be used by it self and/or in conjunction withmesa etching.

FIG. 41 is a cross section view illustrating some further aspects ofMSPD-ASIC monolithic integration, according to some embodiments. Fromthe structure shown in FIG. 40, microstructure holes 4112 are etchedinto the I layer and in some case can be through the I layer to the Nlayer and in some case can be into the N layer and in some cases throughthe N layer. A mesa etch 4160 can also be provided to such that cathodeohmic metal can be deposited on the N region and anode ohmic metal canbe deposited on the P region. Interconnect transmission lines from theMSPD cathode and anode to the TIA/ASICs are not shown. Also not shownare passivation and planarization layers. A metal and/or transparentconducting metal oxide such as ITO and/or silicide and/or dielectricand/or Bragg reflectors/filters 4150 and 4132 can be deposited on the Pand N regions. The metal, ITO and silicide can reduce the sheetresistance and also provide a more uniform distribution of the electricfield to deplete the I layer during reverse bias. A reverse bias of −2to −10 volts can be applied between the anode and cathode. In somecases, the reverse bias is −2 to −4 volts.

The optical signal can impinge from either the top (as shown) and/orbottom surface. In addition, as in FIG. 32, the monolithicallyintegrated MSPD and CMOS ASICs can be solder bumped. In some cases,through substrate vias (TSVs) can be implemented on the monolithicallyintegrated MSPD/MSAPD and CMOS TIA/ASICs such that solder bumps can beattached on the substrate side and attached to the PCB. In this case,using the TSVs, a flip chip configuration can be avoided.

Hole spacing, size, depth, shape, wavelength ranges, QE, responsivity,and data rates can be as described in elsewhere herein, such as inconnection with FIGS. 31, 32, 34, 36, 38. Data rates of 3 Gb/s to 60Gb/s or higher can be attained by the MSPD/MSAPD. Optical signalwavelengths can range from 800-1000 nm and in some cases 800 nm to 1100nm and in some cases 800 nm to 1400 nm and in some cases 800 nm to 1600nm and the QE can be 20% or greater at at least one or more wavelengthsin the range and in some cases the QE can be 50% or greater at at leastone or more wavelength in the range and in some cases the QE can be 70%or greater at at least one or more wavelength in the range.

Hole diameters and/or diagonals and/or width range from 350 nm to 2500nm and in some cases from 400 nm to 3000 nm and in some cases 500 nm to2000 nm and in some cases 500 nm to 1300 nm. Hole spacing can range from10 nm to 3000 nm at the surface and in some cases can intersect at atleast one point with an adjacent hole. Hole diameter/width can vary asdepth and in some cases the diameter/width becomes smaller with depthand in some cases can vary with depth. Holes can be etched wet and/ordry partially into the I layer, through the I layer, to the N or P layerat the bottom, into and/or through the P and/or N layer and in somecases can be etched completely through to the bottom surface.

In addition, the MSPD and MSAPD have very linear output current versesoptical input power. The MSPD have been experimentally observed to havea linear photocurrent-input optical power from less than a mW to over 10mW. Linearity is important for pulse amplitude modulation (PAM-4). See,e.g., Ingham, Future of Short-Reach Optical Interconnects based on MMFTechnologies, OFC 2017 © OSA 2017 (incorporated herein by reference).

Monolithic integration of MSPD/MSAPD with CMOS ASICs is expected tosignificantly reduce the cost of an optical transceiver. See, e.g.,Assefa et al, Monolithically Integrated Silicon Nanophotonics Receiverin 90 nm CMOS Technology Node, OFC/NFOEC Technical Digest © 2013 OSA(incorporated herein by reference), where the authors from IBM state inthe introduction: “Monolithic integration of optical transceivers in astandard CMOS foundry is expected to significantly reduce the cost ofoptical communication links for their wide deployment in datacenters andhigh-performance computing systems . . . ”.

In addition, in some applications in high performance computingwavelength ranges include 900-1100 nm and in some cases 900-1065 nm.See, e.g., Taubenblatt, Optical Interconnects for High-PerformanceComputing, JOURNAL OF LIGHTWAVE TECHNOLOGY, VOL. 30, NO. 4, Feb. 15,2012 (incorporated herein by reference). MSPDs/MSAPDs in Si and/or GeSican address these wavelengths and still be monolithically integrateablewith CMOS/BiCMOS ICs such as TIA and/or ASICs for functions such assignal amplification, conditioning, normalization, processing, storage,transmission and other signal enhancements for error reductionprocessing.

FIG. 42 is a cross section view illustrating aspects of MSPDmonolithically integrated with CMOS/BiCMOS electronics, according tosome embodiments. The CMOS/BiCMOS electronics can be for a TIA and caninclude other ASICs for signal processing, conditioning andtransmission. The microstructure holes 4212 can be etched firstpartially into the low doped and/or undoped I Si and/or GeSi layer withresistivity of 1 ohm-cm or greater and in some cases 10 ohm-cm orgreater and with a thickness ranging from 0.5 to 5 micrometers and insome cases from 0.5 to 2 micrometers. After the microstructure holeetch, the P⁺ (or N⁺ with P and N interchanged from a P-I-N to N-I-P)layer 4284 can be formed conformally to the microstructure holes 4212 byion implantation of the P (or N) type ions and/or by diffusion of P or Ntype dopants. Inverted pyramid holes are shown in FIG. 42 that can bewet etched in KOH solutions and also can be wet etch and/or dry etchedto form holes of different shapes. The bottom N layer 4282 can beepitaxially grown on a SOI wafer with a BOX and in some cases on a Ntype Si wafer without a BOX. Layer 4282 can also be ion implantationand/or diffused with dopants into the device layer of the SOI. In caseswhere a N substrate is used without BOX and the substrate resistivity isin the range of 0.01 ohm-cm or less, the additional doping and N⁺epitaxial layer may not be provided. A N⁺ connecting well 4260 formed byion implantation and/or diffusion can connect the cathode on the surfaceto the N⁺ layer/region 4282 and in the case of a N substrate the cathodecan be on the bottom of the substrate with or without additional connectwells. In some cases a TSV (through silicon via) and/or a deep trenchmay be provided to connect the bottom cathode to the surface ASICs incases where a surface cathode is not available. Not shown, forsimplicity, are the connecting transmission line electrodes from theMSPD/MSAPD to the electronics ASICs.

In all ion implantation situations, multiple energy can be used, andsingle and/or multiple types of ions can be used that can be P typeand/or N type and/or isoelectronic type. Various isolation, formation ofdielectrics and N and P type doped regions can be formed to optimize theperformance of the MSPD and MSAPD.

Recently, experimental results were published on the microstructuredhole silicon photodiode. See, Gao et al, Photon-trapping microstructuresenable high-speed high-efficiency silicon photodiodes, PUBLISHED ONLINE:3 Apr. 2017 I DOI: 10.1038/NPHOTON.2017.37 (incorporated herein byreference and referred to herein as “Gao et al”), which discussed datarates as high as 25 Gb/s attained with quantum efficiency of 50% orgreater at 850 nm. Note that in FIG. 5B of Gao et al, the opticalcurrent verses power is linear to over 25 mW of optical power. Suchlinearity of output current to input optical power makes the MSPDattractive for PAM-4 type multi-level amplitude modulation to increasethe bit rate of a given optical channel.

In addition, the number of holes can be singular and/or multiple and thespacing between holes can vary from 10 nm to 10000 nm and the holes canhave different shapes such as square, rectangle, and/or polygon withdiagonals ranging from 200 nm to 5000 nm and in some cases 500 nm to2500 nm and can be aperiodically and/or periodically arranged on thesurface of the MSPD/MSAPD. In addition, the diameter and/or diagonaland/or a significant measure of dimension of the hole can change withdepth and can range from 0 nm (come to a point such as the point at theapex of an inverted pyramide) to 5000 nm.

The microstructure holes are etched partially into the I or low doped orundoped region, in some cases 10% or less into the I or low dopedregion, and in some cases 20% or less and in some cases 30% or less andin some cases 40% or less and in some cases 50% or less and in somecases 60% or less and in some cases 70% or less and in some cases 80% orless and in some cases 90% or less.

FIG. 43 is a cross section view of a structure similar to FIG. 41 exceptthat the holes are etched through the P-I-N structure, according to someembodiments. The holes 4312 can be bound both top and bottom by air andin some cases at least one side (surface) is bound by a dielectricand/or dielectrics and/or metal.

The bottom surface doping, N type (can be P type with P and Ninterchanged) can be ion implanted with N type ions such as N, P, As,Sb, Bi, C and in some cases the N layer 4082 can be epitaxially grown inwhich case the N layer extends past the via 4030 and is between thesubstrate and the I layer and in some cases can have other layers inbetween such as etch stop layer(s), buffer layers, buried oxide and/ornitride layer(s), amorphous silicon layers, and/or polycrystallinesilicon layers. In addition, with an epitaxial and/or amorphous and/ormicrocrystalline and/or polycrystalline layer(s), ion implantation canstill be used to increase the doping concentration of N (or P) type ionsto reduce lifetime and to reduce sheet resistance.

With the I layer thickness ranging from 300 nm to 3000 nm or thicker,and the P and N layers/regions thicknesses ranging from 100 nm (and insome cases less than 100 nm) to 300 nm (and in some cases more than 300nm), the bulk of the optical absorption occurs in the I layer and canincrease the quantum efficiency. The thin P and N layer/regions 4084 and4082 can have a transparent metal conducting oxide such as indium tinoxide and/or semitransparent metal layer(s) 4050 and 4032 on theirsurfaces to reduce the sheet resistance. Doping concentration of the Pand N layer/region 4084 and 4082 can range from 5×10¹⁸/cm³ to 5×10²⁰/cm³or greater. The higher doping concentrations also reduce the minoritycarrier lifetime and therefore any diffusion of photogenerated carriersin the P and/or N layer/region.

The surface of the holes 4312 can be passivated with native oxide and/ordielectric and/or semiconductor crystalline and/or microcrystallinematerial. The passivation can also be chemical such as with an HFtreatment to reduce surface recombination that can reduce the quantumefficiency. In some cases surface recombination at the surface of holesin the P and/or N layer/region can help reduce the diffusion ofphotogenerated carriers in the P and/or N layer/region into the highfield I region which can degrade the speed/bandwidth response of theMSPD, MSAPD. Thin layer/region of N and P type can reduce the amount ofphotogenerated carriers in the P and N layer/region and therefore reducethe amplitude of the diffused current. In addition with thinner P and Nlayer/region the time to diffuse of the photogenerated carriers in the Pand N layer/region is shorter and therefore the “tail” of diffusioncurrent is correspondingly shorter. Damage due to ion implantation, highdoping levels are all methods that can be used to reduce the lifetime ofminority carriers in the P and N layer/region.

In some cases, the surface of the substrate, that can be N or P type andwith resistivity than can range from 0.1 to 100 ohm-cm for example, canhave a surface ion implant of: N and/or P type ions; O and/or nitrogenions; an inert ion such as Ar, Ne, Xe; and/or ions such as Al, Ni, Pt,Zr, and/or Cr. Such ions can be implanted at and/or beneath the surfaceof the substrate prior to I layer growth where the I layer can have aresistivity of approximately greater than 8 ohm-cm and in some casesgreater than 12 ohm-cm and in some cases greater than 10 ohm-cm and insome cases greater than 5 ohm-cm with a thickness ranging from 500 nm to3000 nm and in some cases to 5000 nm or more. The implanted ions canbehave as an etch stop layer and/or a buried dielectric layer that canalso be used for etch stop and/or as a marker layer when the etching isdry etching and the exhaust is monitored by a mass spectrometer suchthat when it detects Ar and/or Xe and/or other marker ions, then theetching has reached those marker layers. Such methods can be used toprecisely etch the via to the correct depth desired.

In some cases, the I layer can be grown on a SOI wafer where the devicelayer can be a few to tens of ohm-cm resistivity and the buried oxidecan have a thickness ranging from 100 nm to 2000 nm and where the devicelayer can have a thickness ranging from 50 nm to 500 nm and in somecases the device layer can be greater than 500 nm for high resistivitydevice layers with resistivity ranging from 5-30 ohm-cm or greater. TheI layer can be grown on the device layer with resistivity ranging from 3to 30 ohm-cm or higher and thickness ranging from 300 nm to 5000 nm andin some cases from 500 nm to 2500 nm. A via can be etched to the buriedoxide layer on the substrate side and ion implantation can be implantedthrough the oxide layer and into the device and/or I layer. Multiple ionenergies can be used to create a more uniform distribution of dopant inthe device and/or I layer. Single and/or multiple kinds of ions can alsobe used as dopants.

FIGS. 44A-44C are cross section views illustrating some further aspectsof MSPD-ASIC monolithic integration, according to some embodiments. FIG.44A is similar to FIG. 41. An isolation trench 4462 is shown thatelectrically isolates to some extent the MSPD from the CMOS and/orBiCMOS electronics such as TIA and other ASICs. The electrical isolationwould be more complete if the substrate was SOI and the trench 4462 wasetched to the buried oxide. Ion implantation to form region 4482 can beimplemented from the bottom surface by first etching a via 4430 with athickness from the implanted bottom region by 10 or 10 s or less than 10micrometers or so to provide some rigidity during thermal anneal. Thebottom implant can be P or N type ions. In addition in some cases,bottom implant can be achieved by implanting through the top surface andcreate a buried P or N type ions in the bottom region. If ionimplantation for the bottom P or N type region is initiated from the topsurface, then a via will may not be implemented until after thermalanneal and all other processing is complete. A bottom via 4430 can thenbe etched that can provide higher refraction index contrast and alsotransparent metal oxide layer and/or metal layers can be deposited as inFIG. 41 to reduce series resistance and sheet resistance.

In addition in FIG. 44A, P well 4470 and N well 4474 are implanted, Pchannel 4476 and N channel 4472 are also implanted for the CMOS/BiCMOSelectronic transistors. Other layers are not shown for simplicity. See,e.g., Tavernier 2008; Chen et al, A 1.8-V 10-Gb/s Fully Integrated CMOSOptical Receiver Analog Front-End, IEEE JOURNAL OF SOLID-STATE CIRCUITS,VOL. 40, NO. 6, JUNE 2005 (incorporated herein by reference). Data ratesof 5, 10, 25, 50 Gb/s or higher BiCMOS TIA are possible. See, e.g:Kuchta et al, A 55 Gb/s Directly Modulated 850 nm VCSEL-Based OpticalLink, IEEE Photonics Conference 2012 (IPC 2012) Post Deadline Paper PD1.5 (incorporated herein by reference); and Lengyel et al, SensitivityImprovements in an 850-nm VCSEL-Based Link Using a Two-Tap Pre-EmphasisElectronic Filter, JOURNAL OF LIGHTWAVE TECHNOLOGY, VOL. 35, NO. 9, May1, 2017 (incorporated herein by reference), where MSPDs/MSAPDs can beintegrated into such CMOS and/or BiCMOS electronics, ICs for opticalreceiver applications.

In addition, complex micro electro mechanical systems (MEMS) can beintegrated with CMOS electronics. See, e.g., Ghosh et al, On IntegratedCMOS-MEMS System-on-Chip, IEEE-NEWCAS Conference, 2005. The 3rdInternational (incorporated herein by reference); where such processingmethods can be used in the MSPD/MSAPD integration with CMOS ICs foroptical receiver applications.

In addition, FIG. 44A shows a depth etch monitor layer 4466 that can beimplanted with ions such as Ar, Ne, Xe, O, and/or N, so that using amass spectrometer to monitor the exhaust of etching process if such amonitor ion is detected, the etch depth can be determined. Also shownare upper ion implanted region 4484, mesa etch 4460, microstructureholes 4412, and optional ITO, metal, dielectric coatings 4450.

FIG. 44B shows that after bottom ion implantation and thermal anneal(s)in the integration fabrication process, the via 4430 can be furtheretched to the desired depth for optimal or near optimal MSPD (or MSAPD)operation.

FIG. 44C shows that a transparent conducting metal oxide such as indiumtin oxide (ITO), and/or a metal layer and/or dielectric coatings 4432can be used on either the bottom and/or the top surface to reduce sheetresistance.

FIG. 45 is a cross section view as in FIGS. 44A-44C illustrating somefurther aspects of MSPD-ASIC monolithic integration, according to someembodiments. In this example, the via 4430 can be filled with anothermaterial 4532 such as metal, dielectric, poly silicon, amorphous siliconeither fully and/or partially to provide heat sinking and/or possiblyreinforcement of the MSPD/MSAPD structure and CMOS/BiCMOS ICelectronics.

In all of the TIAs, ASICs, and any other electronics described herein,the process can be with CMOS technology and/or BiCMOS technology.Bipolar transistors are known to be able to provide high speed at alarger node. See, e.g., Kalogerakis et al, A Quad 25 Gb/s 270 mW TIA in0.13 μm BiCMOS with <0.15 dB Crosstalk Penalty, ISSCC 2013/SESSION7/OPTICAL TRANSCEIVERS AND SILICON PHOTONICS/7.1 (incorporated herein byreference); Knochenhauer et al, 40 Gbit/s transimpedance amplifier withhigh linearity range in 0.13 mm SiGe BiCMOS, ELECTRONICS LETTERS 12 May2011 Vol. 47 No. 10 (incorporated herein by reference); Nishihara et al,10.3 Gbit/s burst-mode PIN-TIA module with high sensitivity, widedynamic range and quick response, ELECTRONICS LETTERS 31 Jan. 2008 Vol.44 No. 3 (incorporated herein by reference); and Racanelli et al, SiGeBiCMOS Technology for Communication Products, IEEE 2003 CUSTOMINTEGRATED CIRCUITS CONFERENCE (incorporated herein by reference).

FIG. 46 is a cross section view illustrating some further aspects ofMSPD-ASIC monolithic integration, according to some embodiments. Thestarting wafer is a SOI (silicon on insulator) wafer that can have a Ptype device layer of thickness 50-500 nm or more and doping range fromless than 1×10¹⁵/cm³ to greater than 1×10²⁰/cm³ and where to reduce thesheet resistivity, the device layer can be pre selective area ionimplanted and annealed with P (or N) type dopants to a dopingconcentration ranging from 2×10¹⁹/cm³ to 5×10²⁰/cm³ or greater to reducethe series and sheet resistance (region 4682). A via 4630 can be openedon the substrate side for additional ion implantation and anneal tofurther reduce the sheet resistance. The I layer is not intentionallydoped and can have a very low N type and in some cases a P type ionconcentration of less than 2×10¹⁵/cm³ and with a thickness ranging from500 nm to 5000 nm and in some cases more than 5000 nm in thickness, andan N type ion such as P, As, Sb can be ion implanted to form a N typeregion with doping concentration ranging from 1×10¹⁹/cm³ to 2×10²⁰/cm³or greater. Thermal annealing can be used to activate the implantedions. The N type region 4684 thickness can have a range from 50 nm to500 nm and can be covered with a transparent conducting metal oxide suchas ITO 4650 and the microstructured holes 4612 are etch through the ITOand into the I silicon layer and/or I GeSi layer where the Ge fractioncan range from 1% or less to 100% where the layer is all Ge. (In all thediscussions herein of the I layer, the I layer can be Si and/or GeSIalloy with the Ge fraction ranging from less than 1% to 100%).

An electrical isolation trench 4662 is etched between the MSPD/MSAPD andthe CMOS/BiCMOS electronics to minimize electrical interference. Thetrench can be etched to the BOX layer. Also shown in FIG. 46 areimplanted P well 4670 and N well 4674, and P channel 4676 and N channel4672 for the CMOS/BiCMOS electronic transistors.

FIG. 47 is a cross section view illustrating some further aspects ofMSPD-ASIC monolithic integration, according to some embodiments. In thisexample, the MSPD has an I layer that is Si and/or GeSi integrated withCMOS and/or BiCMOS integrated circuits (IC). The circuits can be foramplification and signal processing and can include TIA and other signalprocessing electronics for an application. An SOI substrate with an Ntype device layer with resistivity less than or equal to 0.03 ohm-cm andin some cases greater than 0.03 ohm-cm. See e.g.,http://www.pveducation.org/pvcdrom/materials/general-properties-of-silicon(incorporated herein by reference). In some cases ion implantation of Ntype ions can be implanted to decrease the resistivity of the region4782 below the MSPD to less than and/or equal to 0.002 ohm-cm. The Ntype ion implant can either be implanted from the bottom through the BOXlayer which can have a thickness from 500 nm to 4000 nm and/or from thestarting SOI wafer where selective area ion implantation can be achievedon the device layer and anneal. The MSPD/MSAPD can then be aligned overthe region where the N type ions are implanted and the CMOS/BICMOS canbe over regions where it is not ion implanted with N type ions.

In some cases a buried N or P type region can be created by ionimplanting through the top surface at high enough energy, 200-400 KeVfor example, such that N or P type ions can be implanted in the regionat or near the bottom of the I layer and/or the device layer adjacent tothe BOX for example.

A via 4730 can be etched to the BOX layer and/or before the BOX layerand additional reflector such as metal and/or Bragg reflectors can bedeposited to reflect back the any optical signal that are not absorbed.In addition, the back Si and/or silicon dioxide layer can be patternedwith micro/nanostructures to further improve the enhanced absorption ofthe I layer.

The I layer can be very low doped P or N type, with resistivity greaterthan 2 ohm-cm for N type and greater than 6 ohm-cm for P type, and insome cases greater than 0.2 ohm-cm. The I layer thickness can range from500 nm to 5000 nm. The CMOS/BiCMOS layers can be etched off partiallyand/or completely and P type ions can be implanted at single and/ormultiple energies and single and/or multiple species of ions (alsoapplicable to bottom N type ion implant), to create a P type dopedregion 4784 with thickness ranging from 50 nm to 500 nm and withresistivity less than or equal to 0.002 ohm-cm, and in some casesgreater than 0.002 ohm-cm. A transparent conducting metal oxide such asindium tin oxide layer 4750 can be used on the top surface where theholes 4712 can be etched through to reduce the sheet resistivity. Anelectrical isolation trench 4762 can be etched between the MSPD/MSAPDand the CMOS/BiCMOS ICs. Microstructured holes 4712 can have any shapeand can be periodic and/or aperiodic; the surface diameter and/orsignificant dimension of the holes can range from 300 nm to 3000 nm andin some cases from 400 nm to 2500 nm and in some cases from 500 nm to3500 nm and spacing between nearest neighboring holes can range from 0nm to 5000 nm or more. Hole depth can range from 200 nm to 5000 nm andthe hole can be etched partially into the I layer, and/or through the Ilayer and/or pass the I layer to the bottom N or P type layer and/or tothe BOX (buried oxide) layer. The hole can have a combination of shapessuch as funnel, inverted pyramid, cylindrical, hourglass, spherical, andcombination of shapes at different depth of the hole. Hole depth can beuniform and/or non uniform, hole shape can be the same for each holeand/or different for some and/or all holes, hole diameter can be thesame and/or different for some and/or all holes, hole spacing withadjacent neighboring holes can be the same and/or different for someand/or all holes. This applies to both MSPDs and MSAPDs. In some casesthe microstructure hole depth can range from 50 nm to 5000 nm or morefrom the surface of the semiconductor.

The MSPD is connected to the CMOS/BiCMOS ICs with a transmission line(not shown) and the MSPD/MSAPD can be 10 to 300 micrometers or moreseparated from the CMOS/BiCMOS to reduce optical interference with theCMOS/BiCMOS transistors and other circuit elements. A reverse bias isapplied to the anode and cathode of −2 to −10 volts and in some cases −2to −4 volts for MSPD and −5 to −40 volts for MSAPD. Operating wavelengthrange for Si I layer can range from 750 nm to 1070 nm and for GeSi canrange from 750 nm to 1350 nm and in some cases 900 nm to 1350 nm and insome cases 1100 nm to 1350 nm and in some cases 1250 nm to 1550 nm andin some cases 1250 nm to 1650 nm and in some cases to 2000 nm dependingon the Ge fraction in the GeSi alloy.

Quantum efficiency can be 20% or greater at at least one or morewavelengths in the wavelength span, and in some cases QE can be 30% orgreater and in some cases QE can be 40% or greater and in some cases QEcan be 50% or greater and in some cases QE can be 60% or greater and insome cases QE can be 70% or greater and in some cases QE can be 80% orgreater and in some cases QE can be 90% or greater for MSPD/MSAPD. MSAPDcan have over 100% QE with gain and in some cases over 200% QE with gainand in some cases over 300% QE with gain and in some cases over 400% QEwith gain.

Data rates can range from 5 Gb/s to 60 Gb/s or higher and in some cases10 Gb/s to 25 Gb/s and in some cases 25 Gb/s to 50 Gb/s or more. Alsoshown in FIG. 47 are mesa etch 4760, as well as implanted P well 4770, Nwell 4774, P channel 4776 and N channel 4772 for the CMOS/BiCMOSelectronic transistors.

FIG. 48 is a cross section view illustrating some further aspects ofMSPD-ASIC monolithic integration similar to FIG. 47, according to someembodiments. The N type device layer of the SOI has sufficiently lowresistivity, ranging from 0.005 ohm-cm or less and a thickness rangefrom 100 nm to 500 nm. In some cases the device layer has a resistivityof 1 ohm-cm or more and with a thickness ranging from 50-150 nm, inwhich case an epitaxial growth of a highly doped N layer is needed witha resistivity of 0.005 ohm-cm or less and with the N layer thicknessranging from 100 nm to 500 nm.

The holes 4712 as in FIG. 47 can be etched partially into the I layerand/or through the I layer and/or to the BOX layer (thickness can rangefrom 100 nm to 5000 nm and in some cases 500 nm to 2000 nm). The I layercan be Si and/or GeSi alloy with the Ge fraction ranging from less than1% to 100%.

Light and/or optical signal can impinge from the surface with the holesand in some cases light/optical signal can impinge from the substrateside through a via. The optical signal is brought to the MSPD/MSAPD viaan optical fiber that can have a lens and is focused onto the surfacewith a certain numerical aperture such that there may be an angulardistribution of light rays that are impinging on the surface of theMSPD/MSAPD.

FIGS. 49, 50A and 50B are top views and a cross section viewillustrating some aspects of selective ion implantation for MSPD-ASICmonolithic integration, according to some embodiments. FIG. 49 is a topview showing a starting Si or SOI wafer 4900 where it was masked forselective area ion implantation and where the square or any other shapessuch as rectangular, oval, circular, and any combination of shapes,regions 4982 on the surface are areas that are implanted with P and/or Ntype ions to a resistivity ranging from equal to or less than 0.01ohm-cm to equal to or less than 0.001 ohm-cm following a thermal annealprocess, usually rapid thermal anneal. In addition to the P and/or Ntype regions 4982 selectively implanted with single and/or multiple ionspecies and single and/or multiple ion implantation energies, otherregions 4966 can be implanted with marker ions such as Ar, Ne, Xe, N, O,and/or Al, at the same and/or different energies. Typically higherenergies are used for deeper implants, as an aid for back side viaetching to determine the depth of the etching process by monitoring theexhaust from the etching chamber with a mass spectrometer analyzer. Oncethe marker ions are seen on the mass spectrometer, the approximate depthof the etching can be determined. Further alignment marks 4960 can becreated by etching a mesa or by implanting a metal ion such as Al, Cu,Ni and/or V, so that alignment marks 4960 can be seen by a backsideinfrared illumination and the mask can be placed such that theMSPD/PSAPD is over the N and/or P type implanted areas 4982. Otheralignment marks may also be used for example O and/or N ion implant tocreate an oxide or nitride rich region such that subsequent epitaxialgrowth over the alignment marks can result in a polycrystalline,microcrystalline and/or amorphous Si so that it appears different from ashiny single crystal epitaxial regions.

FIG. 50A is a top view of a Si or SOI wafer shown in FIG. 49 that wasselective area ion implanted, thermally annealed and an I layer 5002 ofSi and/or GeSi and CMOS/BiCMOS layer(s) grown on top of the selectivearea implanted Si or SOI wafer. FIG. 50B is cross sectional view showingthe buried selective area ion implanted regions 4982 and an MSPD/MSAPD5004 fabricated over one of the selective area ion implanted regions4982 and the CMOS/BiCMOS IC 5006 is fabricated over areas not directlyabove regions 4982 that have a buried P and/or N type ions.

FIG. 51 is a cross sectional view of a microstructured avalanchephotodiode (MSAPD) with a P⁺ P⁻⁻PN⁺ structure on SOI wafer, according tosome embodiments. The MSAPD can also be formed on a P or N type siliconwafer, in which case a via (not shown) may be etched on the bottom asdescribed elsewhere herein for MSPD structures. The layer structure forthe MSAPD is similar to that of a conventional silicon APD. See e.g.,WÊGRZECKA et al, Design and properties of silicon avalanche photodiodes,OPTO-ELECTRONICS REVIEW 12(1), 95-104 (2004) (incorporated herein byreference). In the MSAPD structure, some and/or all the layers can be Siand/or GeSi grown either on Si P or N type or SOI wafers. The N⁺ layercan be grown on a SOI wafer with a device layer that is N type forexample and where the device layer thickness can range from 50 nm to 200nm and the N⁺ layer can have a thickness ranging from 100 nm to 500 nm.In some cases, as described herein for MSPDs the device layer can eitherbe selective area implanted with N type dopant and/or implanted from thebottom through a via and through the BOX layer and/or from the topsurface at a high ion acceleration energy and create a buried implantinto the device layer. The N⁺ layer can have a resistivity ranging fromequal to or less than 0.006 ohm-cm. The P layer adjacent to the N⁺ layercan have a thickness ranging from 50 nm to 650 nm with a resistivityranging from 0.2 to 0.06 ohm-cm followed by a P⁻⁻ layer with a thicknessranging from 500 nm to 5000 nm with a resistivity ranging from equal toor greater than 3 ohm-cm followed by P⁺ layer that can be ion implantedwith ions such as B, Al, Ga, In for example with a thickness rangingfrom 50 nm to 500 nm and with a resistivity ranging from equal to orless than 0.002 ohm-cm. The top surface can include a transparentconducting metal oxide such as indium tin oxide (ITO) (not shown) tofurther reduce the sheet resistivity. The microstructure holes 5112 canbe etched through the ITO and partially into the I layer that can be Siand/or GeSi where the Ge fraction can be less than 1% to 100%. The holesare as described elsewhere herein for MSPDs and can have any shapeand/or combination of shapes that include funnel, inverted pyramids,cylindrical, spherical, polygonal, hourglass, and can be etchedpartially into the I layer and/or through the I layer and/or into thebottom P layer and/or to the bottom N⁺ layer and/or to the BOX layer.The hole diameter and/or significant lateral dimension can range from350 nm to 5000 nm and in some cases from 500 nm to 2500 nm and can haveuniform hole diameters and/or non uniform hole diameters and the spacingof the holes with adjacent neighboring holes can range from 0 nm to 5000nm and in some cases from 100 nm to 3000 nm. The cathode is formed onthe N⁺ layer (in mesa etch 5160) and the anode formed on the P⁺ layer.The MSAPD can be operated in a reverse bias mode between the cathode andanode with w voltage range of −6 Volts to −25 Volts. The MSAPD can havea gain of 2 to 10 dB or more and can have a gain bandwidth product of 60Gb/s or higher and in some cases 100 Gb/s or higher and in some cases200 Gb/s or higher and in some cases 300 Gb/s or higher. The operationwavelength can have a range from 750 nm to 1070 nm and in some cases850-950 nm and in some cases 900 nm to 1060 nm and in some cases 950 nmto 1250 nm and in some cases 1250-1350 nm and in some cases 1250 to 1550nm and in some cases 1000 nm to 2000 nm. In some cases, an I layer canbe between the P and N⁺ layer and can be called the multiplication layeras discussed previously in MSAPD structures. In FIG. 51, themultiplication takes place in and around the PN+ interface where theelectric field is the highest.

The light and/or optical signal can impinge from the surface with theholes and in some cases, with a via (not shown), light can impinge fromthe bottom substrate side.

FIG. 52 is a cross section view of a MSAPD integrated with CMOS/BiCMOSICs such as TIA and other ASICS for signal processing, according to someembodiments. As in earlier discussions herein on selective area ionimplantation, the N⁺ layer can be a selective area ion implanted regionin which case only a P layer need to be grown on the substrate followedby P⁻⁻ followed by CMOS and/or BiCMOS layer(s) and the P⁺ region for theMSAPD can be ion implanted with P type ions. In addition in some casesas discussed earlier for MSPD, ion implantation for the N⁺ layer can beimplanted with N type ions from the bottom through a via and through theBOX, in which case the device layer of the SOI can be N or N⁻ doping.

The device layer of a SOI (layer on top of the BOX) is typically lowdoped P or N and can have a thickness ranging from 50-300 nm which isnot shown in FIG. 52 for simplicity. A N⁺ layer is grown on the device Nlayer with resistivity of 0.006 ohm-cm or less and with a thicknessrange of 100-500 nm, followed by a P layer of resistivity ranging from0.07 to 0.3 ohm-cm and a thickness ranging from 50 to 700 nm (in somecases an I layer can be inserted between the N⁺ and P to form a N⁺IPstructure where the I layer can have a resistivity of 0.3 ohm-cm orhigher and in some cases 1 ohm-cm or higher and a thickness ranging from300 to 600 nm) followed by a P⁻⁻ layer with resistivity of 1 ohm-cm orgreater and in some cases 8 ohm-cm or greater and in some cases 30ohm-cm or greater, and with a thickness range of 200 nm to 5000 nmfollowed by P type ion implantation to the top surface of the P⁻⁻ layerto form P⁺ region with resistivity less than or equal to 0.002 ohm-cmand with a thickness ranging from 50 nm to 500 nm. Ion implantation canhave single and/or multiple acceleration energies and can have singleand/or multiple ion species for either the top and/or bottom implantsand/or selective area ion implants. A rapid thermal anneal activate theimplanted ions and anode and cathode and microstructure holes 5212 canbe formed as in FIG. 51.

An electrical isolation trench 5262 is etched as shown in FIG. 52 toisolate the MSAPD from the CMOS/BiCMOS electronics. In some cases, theelectronics can be shielded from stray optical signal with a lightblocking polymer form for example. Other light blocking methods such asmetal, polymer, form can be used. Black polymer form layer can have alow dielectric constant and can be less of a loading factor to the highfrequency microwave signals. The isolation trench 5262 can also bepartially or fully filled with a light blocking material such as apolymer form, and/or dielectric and/or metal layer for example.

Optical signals can impinge from the top (surface illuminated) and/orfrom the bottom through a via (bottom illuminated) and the wholeintegrated chip can be attached to a printed circuit board either holesfacing up or holes facing down using solder bump technology and TSV(through silicon via) to connect the integrated chip electrical andmicrowave connections to the printed circuit board and/or other boardsto external electronics.

A reverse bias is applied to the anode and cathode of the MSAPD withvoltages ranging from −6 volts to −25 volts, in some cases −10 V to−25V.

The diameter of the mesa formed by mesa etch 5260 that defines thejunction area and therefor the junction capacitance can range from 20 to200 micrometers and in some cases 30 to 100 micrometers and in somecases 30 to 80 micrometers for the MSPD/MSAPD structures. The mesa canalso have other shapes such as square, rectangular, polygonal, to name afew. For lower data rate applications, less than 5 Gb/s, the diameter ordiagonal can range from 100 to 500 micrometers. The smaller diametersare mainly for high data rate applications with datarate equal to orgreater than 10 Gb/s and in some cases equal to or greater than 25 Gb/sand in some cases equal to or greater than 50 Gb/s.

FIG. 53 is a top view schematic of an array of MSPDs/MSAPDs integratedwith CMOS/BiCMOS ICs such as TIA and other signal processing ASICs,according to some embodiments. A single chip 5300 with bond pads 5306includes an array of MSPDs/MSAPDs 5310 integrated with electronics 5302.In some cases the electronics 5302 can be a single block withtransmission lines running to different MSPDs/MSAPDs 5310. The number ofMSPDs/MSAPDs 5310 in an array can be 1 to 100 or more and in some casesfrom 2-16 and can be arranged in any fashion. The distance of theMSPDs/MSAPDs 5310 to the electronics 5302 can have a range from 10micrometer or less to 300 micrometers or more, and depends on the sizeof the array and bandwidth of the application and size of theMSPD/MSAPD.

In addition, MEMS (microelectromechanical systems) structures can beimplemented on top and/or below the MSPD/MSAPD such that a tunablefilter can be integrated together on the MSPD/MSAPD and CMOS/BiCMOSelectronics to allow coarse wavelength division multiplexing.

A silicon process allows the integration of MEMS, MSPD/MSA{D andCMOS/BiCMOS ICs to be integrated on a single silicon chip. See e.g., Xieet al, Post-CMOS Processing for High-Aspect-Ratio Integrated SiliconMicrostructures, JOURNAL OF MICROELECTROMECHANICAL SYSTEMS, VOL. 11, NO.2, APRIL 2002 (incorporated herein by reference).

FIG. 54 is a cross section of a possible layer structure for integratingMSPD/MSAPD with CMOS/BiCMOS electronics, according to some embodiments.In the structure shown, a buffer layer of an intrinsic I layer and/orvery low doped P⁻⁻ type layer, often also referred to as a π layerand/or a very low doped N⁻⁻ type layer also referred to as an v layer inthe scientific literature. The very low doping layers can have aresistivity of greater than or equal to 1 ohm-cm and in some casesgreater than or equal to 10 ohm-cm. The Si buffer layer can have athickness range of 1 to 4 micrometers. In some cases, the Si bufferlayer may contain Ge such that it can be GeSi with Ge fraction less thana few percent. The buffer Si (or GeSi) layer can be between theCMOS/BiCMOS layer(s) and the GeSi I layer (which can be low and/or verylow doped P and N type material also with resistivity greater than orequal to 1 ohm-cm.) The GeSi I layer can range in thickness from 0.5 to2 micrometers and in some cases can range from 0.5 to 5 micrometers.Below this I Ge Si layer can be a Si or GeSi N⁺ layer with resistivityless than or equal to 0.006 ohm-cm with thickness ranging from 0.05 to0.5 micrometers. Below the Si of GeSi N⁺ layer is can be an N typedevice layer with thickness ranging from 0.05 to 0.5 micrometers andtypically with a resistivity equal to or greater than 1 ohm-cm. Belowthis can be a BOX layer with thickness ranging from 0.5 to 5 micrometerson top of a handle silicon wafer that can be N type and in some cases Ptype.

According to some embodiments, all herein described ranges and/or valuesin thicknesses, resistivity, doping, ion implant depth and energies,hole diameters/diagonals, hole spacing, hole depth, quantumefficiencies, responsivity, bias voltages, data rates, operationalwavelengths, sheet resistances, photosensitive areas anddiameters/diagonals, capacitances, and any other ranges/parameters arenot fixed and can vary outside the range suggested by from plus or minusa few percent to 50% or more.

The buffer layer may or may not be needed for CMOS/BiCMOS devicefabrication to minimize interference with its standard process. In somecases the BOX may not be needed. In some cases a via (not shown) can beopened to allow further ion implantation into the N and N⁺ layers (insome cases it can be P and P⁺ type layers depending on the MSPD/MSAPDlayer doping structures) and in some cases, the wafer can be selectivearea ion implanted such that the MSPDs/MSAPDs are over the heavily dopedareas of the silicon or SOI wafer.

FIG. 55 is a cross section view illustrating some aspects of MSPD/MSAPDintegration with CMOS/BiCMOS integrated circuits, according to someembodiments. The MSPD(s) and/or MSAPD(s) with the inclusion of anavalanche region(s), are integrated with CMOS/BiCMOS integrated circuitssuch as TIA(s), and/or other signal enhancements and/or processingand/or storage and/or communication ASICs. Many parts are not shown suchas CMOS/BiCMOS transistors, capacitors, inductors, resistors,interconnect layers to form the ICs, transmission line between theMSPD(s)/MSAPD(s) to the ICs, isolation layers, additional transparentconducting metal oxide layer(s) to reduce sheet resistance,anti-reflection coatings, and passivations for simplicity and clarity.

The CMOS/BiCMOS ICs are first processed fully and/or partially followedby the processing of the MSPD/MSAPD. The buffer layer can be etched offand selective area ion implantation, by masking off regions not intendedfor ion implantation with polymer and/or metal layer(s), of P type ionscan be implanted into the I GeSi layer (or Si layer in some cases) toform a highly doped P type region 5584 with resistivity less than orequal to 0.003 ohm-cm with a thickness ranging from 0.05 to 0.3micrometers using single and/or multiple ion implant energies and singleand/or multiple ion implant species. A transparent conducting metaloxide (not shown) can be deposited on the P region to further reduce thesheet resistance. Holes 5512 can then be etched through the transparentconducting metal oxide such as indium tin oxide and into the I GeSi (orin some cases Si layer) as also described herein supra. In some casesthe P and N type can be reversed, where the top implant can be N typeand the bottom layer can be P type. The anode is formed on the P typeregion 5584 and cathode on the N type layer/regions. An electricalisolation trench 5562 can be etched between the MSPD/MSAPD and theCMOS/BiCMOS ICs.

In some cases, the bottom N or P layer can be formed by ion implantationfrom the top surface at high energy creating a buried N or P region. BOXlayer can be used to minimize diffusion current generated outside thehigh field I or low doped regions; however without BOX then an etch stoplayer such as a highly doped P layer can be used when etching vias.

The GeSi I layer or very low doped layer can have Ge fraction rangingfrom a few percent to 100 percent. In some cases the Ge fraction canrange from 1 to 10%, in some cases between 10 and 20%, and in some casesbetween 20-40% and in some cases between 40-80% and in some casesbetween 80-100%.

The microstructured holes 5512 can be etched wet and/or dry partiallyinto the I layer and/or through the I layer and/or to the BOX layer. Theholes can be funnel, cylindrical, rectangular, triangular, polygonal,and can vary in lateral dimension as a function of etch depth. Holediameter, diagonal can range from 300 nm to 5000 nm and in some casesfrom 450 nm to 2500 nm and in some cases from 500 nm to 2500 nm. Holespacing can range from 50 nm to 5000 nm and in some cases from 300 nm to3000 nm. Operating wavelength can range from 750 nm to 2000 nm and insome cases 840 nm to 1065 nm and in some cases 1100 nm to 1350 nm and insome cases 1550 nm to 2000 nm and in some cases from 1200 nm to 1550 nm.Data rates can range from 1 Gb/s to 5 Gb/s and in some cases 1 Gb/s to10 Gb/s and in some cases 5 Gb/s to 25 Gb/s and in some cases 4 Gb/s to10 Gb/s and in some cases to 50 Gb/s or higher. Responsivity can be 0.2A/W or higher at at least one of the wavelengths in the wavelength span.And in some cases 0.1 A/W or higher at at least on wavelength and insome cases 0.3 A/W or higher at at least one wavelength in the span andin some cases responsivity can be 0.5 A/W or higher at at least onewavelength in the wavelength span.

The optical signal can impinge from the top surface where themicrostructured holes 5512 are etched and in some cases the opticalsignal can impinge from the bottom surface through a via (not shown)such as a through a silicon via (TSV).

Additional coatings can be included to further enhance the absorption byreflecting any stray optical signal back toward the microstructure holesas discussed earlier. The coating can be metal and/or dielectric oneither of the top or bottom surfaces.

In addition, the die can contain either a single MSPD/MSAPD andCMOS/BiCMOS electronics or multiple MSPDs/MSAPDs and CMOS/BiCMOSelectronics for parallel optical fiber applications or CWDMapplications. Other applications can include LIDAR, free space opticallinks, sensors, data center optical interconnect, and fiber to the home.

In the integrated MSPD and CMOS/BiCMOS electronics the MSPD is operatedat a reverse bias between the anode and cathode with applied reversebias voltage ranging from −1V to −5V.

Doped regions that are created by ion implantation methods can also becreated using diffusion methods and/or a combination of diffusion andion implantation.

FIG. 56 is a cross section view illustrating some aspects of MSPD/MSAPDintegration with CMOS/BiCMOS integrated circuits, according to someembodiments. The MSPD/MSAPD is integrated with CMOS/BiCMOS electronicsthat are fabricated using standard CMOS/BiCMOS processes. Theelectronics may include additional CMOS/BiCMOS layer(s). The structureuses an I or very low doped P or N type Si layer on an optional BOX. Thebottom N or P type region 5682 can be buried ion implanted and/ordiffusion before the growth of the I layer and/or low doped layer. Insome cases the buried implant can be a selective area implant such thatonly regions under the photodiode is implanted and/or selective areadiffusion. In some cases, a blanket ion implantation and/or diffusionmay be used. Thermal anneal can be used to activate the ion implantedareas with P and/or N type dopants. The buried N or P layer 5682 can beclose to the BOX layer, when a BOX layer is included. The buried N or Player 5682 can have a resistivity of less than or equal to 0.01 ohm-cmand in some cases less than or equal to 0.002 ohm-cm. The buriedimplanted region 5682 can have a thickness of 100 nm to 500 nm. In somecases the buried N or P type layer 5682 can be doped using a diffusionmethod instead of ion implantation and the diffusion of dopants can beselective area diffusion. The N or P doped region 5682 can then beburied by the growth of the I or low doped layer. In some cases, duringepitaxial growth, some dopant may diffuse into the I or low dope region.See, e.g., Swoboda. The I or low doped region can have a layer thicknessranging from 0.5 to 5 microns and in some cases 0.5 to 2 microns and aresistivity in the neighborhood fo 1-10 ohm-cm or greater.

The top surface layer 5684 can be P (or N) type ion implantation and/ordiffusion also with resistivity less than or equal to 0.002 ohm-cm witha thickness ranging from 100-500 nm. In addition a transparentconducting metal oxide can be used on the top surface to further reducethe sheet resistance.

The microstructured holes 5612 can be etched wet and/or dry partiallyinto the P or N doped region and/or partially into the I layer or lowdoped P or N layer, and/or through the I layer or low doped P or Nlayer, and/or to the BOX layer and/or to the bottom doped layer in thecase without a BOX. The holes 5612 can be funnel, cylindrical, invertedpyramid, ball shaped, rectangular, triangular, polygonal, and can varyin lateral dimension as a function of etch depth. Hole diameter,diagonal can range from 300 nm to 3500 nm and in some cases from 450 nmto 2500 nm and in some cases from 500 nm to 2500 nm. Hole spacing canrange from 50 nm to 3500 nm and in some cases from 300 nm to 3000 nm.Operating wavelength can range from 750 nm to 1065 nm and in some cases840 nm to 1065 nm and in some cases 950 nm to 1065 nm and in some cases840 nm to 1100 nm. Data rates can range from 1 Gb/s to 5 Gb/s and insome cases 1 Gb/s to 10 Gb/s and in some cases 10 Gb/s to 25 Gb/s and insome cases 4 Gb/s to 10 Gb/s and in some cases 25-50 Gb/s or higher.Responsivity can be 0.2 A/W or higher at at least one of the wavelengthsin the wavelength span. And in some cases 0.1 A/W or higher at at leaston wavelength. And in some cases 0.3 A/W or higher at at least onwavelength. And in some cases 0.4 A/W or higher at at least onwavelength. And in some cases 0.5 A/W or higher at at least onwavelength.

The integrated MSPD is operated at a reverse bias between the anode andcathode with a reverse bias voltage ranging from −1 V to −5 V.

The integrated MSPD/MSAPD and CMOS/BiCMOS electronics can be a single ormultiple MSPD/MSAPD and electronics for parallel fiber and/or CWDMapplications. Other applications can include LIDAR, free space opticalcommunication, data center optical interconnect, high performancecomputing, fiber to the home, sensors, and Lifi.

The optical signal can impinge from the top, surface illuminated, and/orfrom the bottom through a via (not shown).

The photosensitive region of the MSPD/MSAPD can be circular,rectangular, polygonal, quarter circle, or any other shape. For circularphotosensitive the diameter can range from 10 micrometer to 500micrometer or more depending on the application and data rate needed.For data rates of 10 Gb/s to 25 Gb/s the diameter can range from 20micrometer to 80 micrometer or more for example. For lower data rateapplications, larger area MSPD/MSAPD can be used with diameter rangingfrom 50 to 500 micrometers or more.

In some cases, using a standard CMOS wafer and fabricating a siliconphotodiode as discussed in Tavernier 2008, the responsivity at 850 nmwas reported as 5 mA/W. With the addition of microstructured holes tothe silicon photodiode, the responsivity can be significantly improvedby several factors and in some cases by order of magnitude or more. Withthe addition of microstructured holes, the absorption of siliconphotodiodes can be enhanced and extend the operational wavelength to 900nm and in some cases to 990 nm and in some cases to 1065 nm and in somecases to 1100 nm and in some cases to 1170 nm. See, e.g., Tavernier2008. With the addition of a few percent or more of Ge to form a GeSi Ilayer, the wavelength can be further extended beyond 1170 nm.

FIG. 57 is cross section view of a CMOS/BiCMOS wafer on SOI for use inintegration with MSPDs/MSAPDs, according to some embodiments. Thestructure has a low doped P⁻⁻ layer on a P device layer. The resistivityof the P⁻⁻ layer can be equal to or greater than 1-10 ohm-cm and in somecases equal to or greater than 20 ohm-cm, with a thickness of 0.5 to 5micrometers and in some cases 1-3 micrometers and in some cases 0.5-2micrometers. A buried P⁺⁺ well 5704 with resistivity that can be equalto or less than 0.01-0.001 ohm-cm, can be ion implanted and/or diffusedas in Swoboda, close to the BOX layer with a thickness ranging from 0.1to 0.5 micrometers and/or entirely the P device layer. As in Swoboda,the buried P⁺⁺ region 5704 can be formed by epitaxially growing the I orlow doped layer subsequently. The buried P⁺⁺ region can be selectivearea and/or blanket area. A P⁺⁺ connecting well 5706 with resistivityequal to or less than 0.01-0.001 ohm-cm, can be implanted or diffused tointercept and/or in close proximity to the buried P⁺⁺ well 5704 which insome cases may require multiple epitaxial growth as discussed inSwoboda, and form the outside circumference of the photosensitive area.A N⁺⁺ well 5784 can be ion implanted or diffused on the top surface,with resistivity less than or equal to 0.01-0.005 ohm-cm and a thicknessranging from 0.05 to 0.5 micrometers. In some cases a thinsemitransparent metal layer (not shown) such as Pt, Au, Cu, V, Ni, Ag,Al, and/or Cu, with thicknesses ranging from 1 nm to 50 nm and/ortransparent conducting metal oxide with thickness in the range of 10 nmto 1000 nm, can be deposited on the N⁺ region prior to hole etch. TheN⁺⁺ doped region 5784 defines the photosensitive area of the MSPD andcan be circular, square, polygonal and/or any combinations of shapeswith lateral dimensions such as diameter and/or diagonal ranging from20-1000 microns and in some cases from 20 to 100 microns and in somecases 30 to 100 microns.

Thermal annealing can be done together with CMOS/BiCMOS thermal annealstep to activate the P and N type ion implanted regions or in some casesit can be thermally annealed prior to CMOS/BiCMOS device processing.See, e.g., Huang et al, A 10-Gb/s OEIC with Meshed Spatially-ModulatedPhotoDetectorin0.18-umCMOSTechnology, IEEE JOURNAL OF SOLID-STATECIRCUITS, VOL. 46, NO. 5, MAY 2011 (incorporated herein by reference andreferred to herein as “Huang et al”), which shows a deep N well, whichin some cases may require multiple epitaxial growth, connected to an Nwell (FIG. 6 of Huang et al). See also: Tavernier et al, High-SpeedOptical Receivers With Integrated Photodiode in 130 nm CMOS, IEEEJOURNAL OF SOLID-STATE CIRCUITS, VOL. 44, NO. 10, OCTOBER 2009(incorporated herein by reference and referred to herein as “Tavernier2009”), which shows a surface N well; Kao et al, A 5-Gbit/s CMOS OpticalReceiver With Integrated Spatially Modulated Light Detector andEqualization, IEEE TRANSACTIONS ON CIRCUITS AND SYSTEMS—I: REGULARPAPERS (incorporated herein by reference and referred to herein as “Kaoet al”), which shows a spatially modulated photodetector with guardrings; Youn et al, which shows a P in an N well avalanche photodiode;Hartman et al, A Monolithic Silicon Photodetector/Amplifier IC for Fiberand Integrated Optics Application, Journal of Lightwave TECHNOLOGY, VOL.LT-3, NO. 4, AUGUST 1985 (incorporated herein by reference), which showsa PIN photodiode integrated with IC electronics; and Radovanovic′ et al,A 3-Gb/s Optical Detector in Standard CMOS for 850-nm OpticalCommunication, IEEE JOURNAL OF SOLID-STATE CIRCUITS, VOL. 40, NO. 8,AUGUST 2005 (incorporated herein by reference), which shows aninterdigitated silicon photodiode. Swoboda shows a PIN siliconphotodiode integrated with TIA and other ASIC electronics.

The Si photodiode structures in these references can be used with theaddition of microstructure holes and/or other microstructures such asmicrostructure optical waveguide photodetectors as in FIG. 61, infra, toenhance the absorption and further improve its performances and perhapsuse less complex electronics for signal processing. A higher signal tonoise ratio can be desirable and the system can be more stable inadverse operating conditions such as high temperatures environments indata centers and high performance computing and LIDAR for example. Inaddition, low reverse bias voltages for MSPD in the range −1 to −4V andMSAPD in the range −6 to −25 V can be desirable for reliable systemoperation and/or compatible with CMOS/BiCMOS voltages. The dotted line5702 represents the depletion when a reverse bias is applied to theanode and cathode (not shown).

FIG. 58 is cross section showing some aspects CMOS/BiCMOS integrationwith MSPDs/MSAPDs, according to some embodiments. The layer structuresand implanted and/or diffused regions as shown in FIG. 57 are used.Shown is a monolithically integrated MSPD in a N-I-P configuration withCMOS/BiCMOS TIA and any other signal processing, enhancing, transmittingASICs into a single chip. Note that although the layer structures andimplanted and/or diffused regions shown in FIG. 57 are used, the ionsactivation by rapid thermal annealing can occur before, during or afterthe CMOS/BiCMOS processing is partially and/or fully completed.Microstructured holes 5812 can be etched into the top surface with depthranging from 100 nm to 10000 nm and in some cases from 200 nm to 5000 nmand in some cases 500 nm to 2500 nm and in some cases 500 nm to 1100 nm.The holes can be partially into the N region 5784, and/or partially intothe I or low doped high field I or P⁻⁻ region and/or through the lowdoped region and and/or to the P⁺ doped region 5704 and/or to the Boxlayer. The holes 5812 can be circular, square, polygonal, oval, amoeba,hourglass or other shape. The lateral dimension,diameter/diagonal/significant length of the holes can range from 200 nmto 5000 nm and in some cases from 450 nm to 2000 nm and in some cases500 nm to 1650 nm. Spacing between holes can range from 50 nm to 3000 nmand in some cases from 100 nm to 2000 nm. The holes cross section can beof any shape, for example funnel, inverted pyramid, cylindrical, Vshape, polygonal, ball like, hourglass, and/or any combination of shapesthat can be dry and/or wet etched and/or electrochemically etched. Theholes can be period, aperiodic and/or combination of periodic andaperiodic. In some cases prior to hole etch, a layer of transparentconducting metal oxide (not shown) can be deposited on the N surface toassist in the reduction of sheet resistivity. The N and P type can bereversed to form an P-I (P⁻⁻ or N⁻⁻ region) on N and for MSAPD a chargeand multiplication region can be added). The cathode and anode can beformed on the surface and the device for MSPD is operated at a reversebias voltage ranging from −1 to −5 volts and for MSAPD the reverse biasvoltage can range from −6 to −30 volts. The cathode and anode areconnected to the TIA and/or other ASICs and can include an inductorand/or other circuit elements in the transmission line and/or ASICs suchas equalizers for peaking the frequency response of the photodiodeintegrated with TIA and other ASICs. Passivations, planarization, metalinterconnects, transistors, capacitors, resistors, inductors, memoryelements, to name a few are not shown.

An optical and/or electrical isolation or attenuation region 5860 can beincluded to avoid light interference with the IC electronics. Thisisolation region can be a trench, and/or an ion implanted region tocreate an amorphous semiconductor region where it has poor electricalconductivity and high optical absorption. It can also be implanted withO, N ions and/or metal ions.

Light can impinge from the surface where the holes are etched and/orfrom the bottom where a via (not shown) can be etched to the BOX layer.

By etching microstructured holes 5812, the absorption of light atwavelengths 800-1170 nm can be significantly enhanced for Si and/or GeSiwhere Ge fraction is less than 0.1 and in some cases less than 0.2 forexample. For example, in Tavernier 2008, at 850 nm the responsivityobserved was 5 mA/W whereas with absorption enhancing microstructuredholes and microstructured optical waveguides, 350 mA/W can be observed.At 1000 nm wavelength responsivity of 150 mA/W have been observed on Siphotodiodes with microstructure holes for absorption enhancements andcan reach data rates in excess of 20 Gb/s. Data rates of 25 Gb/s and 50Gb/s can be achieved with equalization, and other electronic signalconditioning methods for silicon photodiodes with microstructured holesat wavelength range from 800-1000 nm and in some cases from 840 nm to1100 nm.

With the addition of Ge to form GeSi alloy the wavelength can be furtherextended to 1350 nm and in some cases to 2000 nm depending on the Gecontent and can also depend if the layers are relaxed or not relaxed.

In some cases the MSPD/MSAPD can be fabricated on a silicon wafer andwhere a BOX layer and/or SOI wafer may not be needed and in some cases aburied oxide layer can be implemented by ion implantation of O ions intothe silicon substrate and can be a blanket implant and/or selective areaimplant followed by a second buried implant and/or diffusion ofshallower depth of P or N type dopants that can be thermally anneal toactivate the dopants and recrystallize the Si if necessary followed byepitaxial growth of the I or low doped layer. The purpose of the buriedO implant is to reduce the photogenerated carrier lifetime that aregenerated outside the high electric field region and may diffuse slowlyback to the high field region that may result in a slow component in theimpulse response of the MSPD/MSAPD. The buried O ions can have a dopingrange of 1E18 to 1E21 and the P or N buried dope layer can have aresistivity in the range 0.01 to 0.001 ohm-cm or less and a thicknessrange of 100 nm to 500 nm. In addition a back side via is an option forbackside optical signal illumination. This can also apply to any otherfigures herein where a BOX is included.

In known references on integration of silicon photodiode and TIA andother electronics, such as Huang et al, which presented a summary ofsilicon photodiode integrated with TIA and additional ASICs for signalenhancement and processing, the responsivity, photodetector bandwidthand bias voltage can be key parameters. In many cases the responsivityis either too low, thus requiring low noise amplifiers of several stageswhich can increase power consumption, or more sensitive to noise due toa low signal to noise ratio caused by, for example, hot environments orelectromagnetic interference. Low photodetector bandwidth may lead tothe use of significant signal processing electronics to achieve goodresponsivity, which can further reduce the responsivity at highfrequency and in many cases high bias voltages. See. e.g., Swoboda,where their P-I-N silicon photodiode had a 10 micrometers thick I layerto achieve a responsivity of 260 mA/W at 850 nm and a data ratebandwidth of 2.2 GHz, required a bias voltage of −17V.

With the addition of microstructured holes on a silicon photodiode, asdisclosed in herein, a thinner I layer can be used to achieve a highresponsivity due to absorption enhancements, resulting in high data ratebandwidth, high responsivity and low bias voltage which are desirablefor low power consumption electronics, high signal to noise ratio andhigh data rate bandwidth that can simplify electronics resulting in amore stable system in adverse environments.

FIGS. 59A and 59B are cross sections illustrating some aspects of a MSPDintegrated with CMOS/BiCMOS ASICs that include a TIA on a CMOS/BiCMOScompatible silicon substrate, according to some embodiments.

FIG. 59A shows a N type substrate, 0.5-5 micrometer thick N⁻⁻ layer withresistivity equal to or greater than 1 ohm-cm and in some cases greaterthan or equal to 10 ohm-cm, is epitaxially grown on buried N⁺ implantedand/or diffused region 5904 and oxygen ion implanted region 5934 belowthe N⁺ region 5904 in the N substrate. In some cases if the N substrateresistivity is 0.01 ohm-cm or less, the N⁺ buried implant may not benecessary. Further CMOS/BiCMOS layer(s) may be formed. As discussed inSwoboda, there may be no further CMOS/BiCMOS layers (see, e.g., FIG.13.5.1 of Swoboda). It may also be the case for some other MSPDs/MSAPDsintegrated with CMOS/BiCMOS ICs that no further CMOS/BiCMOS epitaxiallayers are necessary and the layer(s) maybe just be low doped N⁻⁻ or P⁻⁻type layer(s) with resistivity greater than or equal to 1 ohm-cm and insome cases greater than or equal to 3 ohm-cm. In some cases, extraCMOS/BiCMOS layers will be provided such as where GeSi is used in thetransistor process.

In FIG. 59A, a P-I-N MSPD is formed with buried N⁺⁺ type well 5904implanted/diffused and N⁺⁺ type connecting well 5906 that can beimplanted and/or diffused and a P⁺⁺ type well 5984 that can be implantedor diffused. The N⁺⁺ type wells can have resistivity equal to or lessthan 0.004 ohm-cm and the P⁺⁺ type well can have resistivity equal to orless than 0.004 ohm-cm. The depth of the deep N⁺⁺ type well, which mayrequire multiple epitaxial growths, can range from 0.5 to 5 micrometersand in some cases from 0.5 to 2 micrometers and in some cases 0.5 to 2.5micrometers. The microstructured holes 5912, including their size, shapeand spacings are as described elsewhere herein, and can be etched wetand/or dry into the P⁺⁺ layer and/or partially into the N⁻⁻ layer and/orpartially into the N⁺⁺ layer and/or through the N⁺⁺ layer. In some casesa transparent conducting metal oxide such as indium tin oxide layer canbe applied to the top surface prior to hole etching to assist inreducing the sheet resistivity.

In some cases, N⁺ buried layer 5904 may not be necessary if the Nsubstrate resistivity is 0.01 ohm-cm or less.

The dotted line 5902 represents the depletion when a reverse bias isapplied to the anode and cathode. Reverse bias voltages can range from−1 to −5V and in some cases −1 to −3.3 V.

In some cases, a deep buried ion implantation of oxygen ions and/ornitrogen ions can be used to create a buried oxide and/or oxygen richlayer and/or a nitride and/or a nitrogen rich layer 5934. This buriedoxide and/or nitride layer 5934 can be to reduce photogenerated carriersoutside the high field region which can create a slow diffusion currentthat can degrade the bandwidth of the MSPD/MSAPD. In addition such aburied oxide and/or nitride layer 5934 can also help reflect any straysignal photons back toward the microstructured holes for furtherabsorption enhancements. In some cases ions such as O, N and/or metalions such as Al, Cu, Be, and/or Mg create a disorder region such thatoptical absorption and recombination of minority carriers time is shortto reduce diffusion current generated away from the high field depletionregion. In some cases, the implants can be buried by multiple epitaxialgrowths where the ions are first implanted and followed by epitaxialgrowth to bury the implant. Doping density of the O, N and other ionscan range from 1E18/cm³ to 1E22/cm³ for example. In some cases, theburied O, N and/or other ions for reducing minority carrier lifetimesmay not be provided. Other methods may be the use of heavily doped N orP regions with resistivity less than 0.01-0.001 ohm-cm to reduceminority carrier lifetimes. In some cases, PN junctions, single and/ormultiple such as PNPNPNPN may be used to impede minority carriers fromdiffusing back to the high field region of the I layer/region.

The optical signal can impinge from the surface, surface illuminated,where the holes are etched and/or from the bottom through a via.

The optical signal wavelength can range from 810 nm to 1100 nm and insome cases 750 nm to 1100 nm and in some cases 840 nm to 1070 nm andwhere the responsivity can be 100 mA/W or higher at at least onewavelength in the range, and in some cases 200 mA/W or higher at atleast one wavelength in the range and in some cases 300 mA/W or higherat at least one wavelength in the range and in some cases 400 mA/W orhigher at at least one wavelength in the range and in some cases 500mA/W at at least one wavelength in the range. Data rate bandwidths canrange from 1-50 Gb/s or higher and in some cases 15-25 Gb/s or higherand in some cases 25-50 Gb/s or higher and in some cases 1-25 Gb/s orhigher. Diameter/Diagonal of the photosensitive area can range from15-500 micrometers or more and in some cases 30-100 micrometers.

As discussed herein supra, the MSPD/MSAPD integrated with TIA and othersignal processing/storage/transmitting ICs can be single and/ormultiple, for example a quad for parallel fiber links where theaggregated signal is 4× that of a single MSPD/MSAPD and ICs, it can be16×, 32×, or 64×.

The MSPD and TIA and other ASICs integration can also apply to MSAPDsand TIAs and other ASICs with the addition of a charge andmultiplication layers such that instead of a P-I-N, it can be P-I-PN orP-I-P-I-N as described elsewhere in this disclosure. See e.g., Youn etal. According to some embodiments, Si avalanche photodiodes withmicrostructured holes can have higher data rate bandwidth, higherresponsivity and lower reverse bias voltage than a comparable Siavalanche photodiode without microstructured holes for enhancement ofthe absorption of the optical signal photons.

FIG. 59B shows a simple cross section of a MSPD integrated with TIA andother ASICs similar to FIG. 59A with the addition of an isolation trench5960 that can have a depth ranging from 0.1 to 10 micrometers and canhave a width of 0.1 to 10 micrometers or more that can be around theMSPD and/or MSAPD completely or partially. In addition, it can be asingle trench as shown and/or multiple trenches and in some cases thetrench spacings and width can satisfy the Bragg condition for adistributed Bragg reflector. The trench can be for electrical and/oroptical isolation. In some cases, the trenches can be filled fullyand/or partially with a dielectric and/or polymer and/or metallicmaterial and/or metallic like material.

FIG. 60 is a cross section view of a silicon PIN photodiode integratedwith TIA and other ASICs, according to some embodiments. Note that manyof the cross sections shown in this disclosure have been simplified forpurposes of clarity. Techniques according to embodiments of thisdisclosure are used to modify a structure disclosed in Swoboda. In FIG.13.5.1 of Swoboda the distance between the top surface P⁺ region andburied N⁺ region is about 10 micrometers and a reverse bias voltage of−17 V is used to reach a bandwidth of 2.2 GHz. According to someembodiments of this disclosure, microstructured holes 6012 are etchedwet and/or dry, as a back end of the line (BEOL) CMOS/BiCMOS processand/or as a part of the CMOS/BiCMOS trench processes. By etching themicrostructured holes, the silicon photodiode is converted to a MSPDwith absorption enhancement. The thickness between the P⁺ and N⁺ regioncan be reduced to 1-5 micrometers and in some cases from 0.5 to 3micrometers and in some cases 0.5-2 micrometers. With N⁻ regionsresistivity in the range 1-10 ohm-cm or greater, a reverse bias voltageof −2 to −4 V can deplete the N− region. In some cases a reverse biasvoltage of −2 to −3.3 V can deplete the N− region of 0.5-2 micrometersapproximately. In some cases a reverse bias voltage of −2 to −3.3 V candeplete the N− region of about 1 micrometer, in some cases about 2micrometers, and in some cases 0.5-5 micrometers. The microstructuredholes 6012 can be etched such as described herein supra. The holes 6012can have cross sectional shapes such as funnel, inverted pyramid,cylindrical, trapezoidal, polygonal, hourglass, ball and/or anycombination of shapes. The holes can have diameter/diagonal/significantlateral dimensions ranging from 350 nm to 2000 nm, from 500 nm to 1700nm and in some cases 250 nm to 3000 nm. The holes can have spacing from50 nm to 3000 nm and in some cases 100 nm to 2000 nm. The etch depth canrange from 100 nm to 2000 nm, from 200 nm to 2500 nm, from 250 nm to6000 nm, and in some cases from 50 nm to 5000 nm. The holes can bepartially in the P⁺ region and/or first doped region, and/or partiallyinto the N⁻ region and/or low doped region and/or intrinsic region,and/or partially into the N⁺ region and/or the second doped regionand/or through the second doped region. With microstructured holes theresponsivity can be 100 mA/W or higher for at least one wavelength inthe range 800 nm to 960 nm, and in some cases from 840 nm to 1100 nm.Responsivity can be 200 mA/W or greater for at least one wavelength inthe range 800 nm to 1100 nm, and in some cases responsivity can be 300mA/W or greater for at least one wavelength in the range 800 nm to 1100nm. In some cases responsivity can be 400 mA/W or higher for at leastone wavelength in the range 800-1100 nm. In some cases responsivity canbe 500 mA/W or higher for at least one wavelength in the range 800-1100nm.

Data rate bandwidths can range from 1-5 Gb/s and in some cases 3-10 Gb/sand in some cases from 10-25 Gb/s and in some cases 25-50 Gb/s and insome cases 50-100 Gb/s or higher from the monolithically integrated MSPDand TIA and ASICs chip.

Diameter/diagonal of the MSPD photosensitive area and/or area definingthe capacitance of the P-I-N or N-I-P structure, (lateral width of theN⁺ region and/or first doped region, and/or width of the mesa) can rangefrom 20 to 100 micrometers, in some cases 30 to 80 micrometers, in somecases 100 to 500 micrometers, and in some cases 10 microns to 1000microns. Also shown in FIG. 60 are P⁺ anode 6012, N⁺ cathode 6022 andantireflection coating 6050. The dash lines in FIG. 60 representmultiple epitaxial layer growths as discussed in Swoboda.

Without microstructured holes, as discussed in Swoboda, silicon PINphotodiodes can achieve a responsivity of 260 mA/W at 850 nm wavelengthfor the 10 micrometer thick I or N− region resulting in a 2.2 GHzphotodiode bandwidth at −17V bias. Complex signal processing electronicsare required to achieve a 11 Gb/s data rate bandwidth resulting in ahigh power consumption of 310 mW. Such high reverse bias and powerconsumption are not desirable. In addition, such a structure will bedifficult to push the “chip” (integrated PD and TIA and ASICs) bandwidthto 25 Gb/s. Whereas, using embodiments of this disclosure, with thinnerI layer of 0.5-2 microns together with microstructure holes and/ormicrostructure optical waveguides as in FIG. 61, infra, for photontrapping and absorption enhancements, chip data rate output of 25, 50,80 and 100 Gb/s can be achieved.

In some cases the resistivity of the P⁺ and/or N⁺ regions discussedearlier and thereafter, can be 0.1 ohm-cm or less, and in some cases0.01 ohm-cm or less and in some cases 0.001 ohm-cm or less. N- andP-regions, the low doped regions and/or intrinsic regions, can haveresistivity or 0.2 ohm-cm or greater and in some cases 1 ohm-cm orgreater and in some cases 10 ohm-cm or greater.

Csutak et al, High-Speed Monolithically Integrated SiliconPhotoreceivers Fabricated in 130-nm CMOS Technology, JOURNAL OFLIGHTWAVE TECHNOLOGY, VOL. 20, NO. 9, SEPTEMBER 2002 (incorporatedherein by reference) shows a lateral P-I-N. According to someembodiments of the present disclosure, microstructured holes can beetched in an I region of a lateral P-I-N structure which will enhancethe absorption of optical signal and improve the responsivity.

Note that in Swoboda, two epitaxial growths represented by the dottedlines are grown to bury the deep N⁺ and P Isolation regions that can beformed by diffusion of dopants and/or ion implantation. The secondepitaxial growth is used form the connecting N⁺ wells of the P-I-Nphotodiode and the elements for a bipolar transistors for the TIA andequalizer ICs. In Swoboda, however, the thickness of the 10 micron Ilayer limits to chip data rate bandwidth to 11 Gb/s.

FIGS. 61A-61D is a top views illustrating aspects of microstructuredoptical waveguides, according to some embodiments. In FIG. 61A, a basicmicrostructured optical waveguides (MSOW) structure is shown. In amaterial 6000, a number of holes 6110 are formed. The holes 6110 areconfined within a region 6102, marked with dashed line. At the core ofthe region 6102 there is a region 6112 marked with a dotted line that isfree of holes 6110. The MSOW is formed by a high optical refractiveindex, hole-free core region 6112 surrounded by a region 6102 that a lowoptical refractive index due to the presence of holes 6110. The lateraldimensions of the core region 6112 ranges from sub optical wavelengthsto tens of optical wavelengths. FIGS. 61B and 61C show further MSOWexamples, in this case where the core(s) 6112 are closer to the size ofthe holes 6110. FIG. 61D is a wider view wherein the individual holes6110 are not shown for clarity. In that example several MSOWs are shownin close proximity to one another on an isolated mesa 6150. Two of theMSOWs have a single central core such as shown in FIG. 61A. Otherexamples of MSOWs are shown that have larger cores, non-centered cores,and multiple cores in various arrangements.

The close proximity of the MSOWs allows cross coupling of the opticalfields of adjacent microstructured optical waveguides thereby promotinga collective ensemble of coupled microstructure optical waveguides withoptical waves propagating laterally. This results in absorptionenhancements of the signal photons by the silicon photodiodes withmicrostructured optical waveguides or microstructured optical waveguidephotodiodes (MSOWPDs) and equivalently a microstructured opticalwaveguide avalanche photodiode (MSOWAPDs). As used herein the terms“microstructure hole” and “microstructure photodetector” can also referto MSPD, MSOWPD, MSAPD and MSOWAPD.

For silicon I and/or low doped layer, where I can represent undoped,intrinsic and low doped, the wavelength can range from 800-1100 nm, andin some cases from 840 to 960 nm and in some cases from 840 to 1070 nm.Microstructure holes 6110 can have shapes which are circular, oval,rectangular, polygon, hourglass and/or any other shapes and/orcombination of shapes. The holes can have a lateral dimension, diameter,diagonal, ranging from 300 nm to 5000 nm. The core 6112 can be circular,rectangular, polygonal, oval and/or any other shapes and/or combinationof shapes. The core can have a lateral dimension, diameter, diagonalranging from 200 nm to 4500 nm and a single microstructure hole can havea single and/or multiple cores of same and/or different diameters forexample.

For GeSi I or low doped layer, depending on the Ge fraction, thewavelength can range from 800 nm to 2000 nm. For Ge fraction less thanor equal to 50%, the wavelength span can range from 800 nm to 1350 nmand for Ge fraction less than or equal to 80% the wavelength can rangefrom 800 nm to 1550 nm and for 100% Ge fraction the wavelength can beextended to 2000 nm. For high data rate applications of 10 Gb/s orgreater and in some cases 25 Gb/s or greater, the thickness of the I orlow doped layer can range from 0.5 to 5 micrometers and in some cases 1to 3 micrometers and in some cases 1 to 2 micrometers. The thinner Ilayer is not only for high data rate but also for low voltage reversebias, since in most system, the voltage range from 1 to 5 V and in somecases 1 to 3.3 volts.

For lower data rate applications, I layer thickness of 3-5 micrometersmay be used together with a larger photosensitive area, for example adiameter or diagonal of 100 micrometer or larger. For high data rateapplications, data rates of 10-50 Gb/s the diameter/diagonal of thephotosensitive area can range from 20 to 80 micrometers. In some cases25 to 50 micrometers.

Within a photosensitive area of an MSPD or MSAPD (such as a mesa 6150shown in FIG. 61D), the microstructured optical waveguides can havedifferent configurations, for example with single or multiple cores,cores diameter can be different, the confining microstructure hole canbe different shape and/or dimensions, and the core and/or the MSOWs cancan periodic and/or aperiodic and/or any combination of shape,dimensions, number of cores. These variation can result in aresponsivity vs wavelengths that is smoother and has less undesirableresonances.

The photosensitive area can be defined by a mesa and/or a diffused P orN region and can be circular, oval, rectangular, triangular, hour glass,polygon and/or any other shapes and combination of shapes. In somecases, it can be a single photosensitive area and/or a multiple ofphotosensitive areas such as an array that can be a stand-alone arrayand/or the array can be integrated with CMOS/BiCMOS ASICs for signalprocessing, image processing, sensings, for applications such as opticaldata communications, LIDAR, LiFi, and free space optical communications.

The hole-free areas 6112, shown as a dotted circles, form an opticalwaveguide, and can also be a photonic crystal waveguide and/or in somecases where the holes are not regular, and/or periodic, and/or a certainsize, can be a guided refractive index waveguide. In some cases theoptical mode in the waveguide can interact with optical modes in theholes to generate photon trapping and/or slowing effects for example.Single and/or multiple such waveguides can be provided can also coupleto each other and the holes dimensions and periods around each waveguidecan be same and/or different from adjacent waveguides and can beperiodic and/or aperiodic and/or combination of periodic and aperiodic.

FIG. 62A is a cross section view showing aspects of a microstructuredoptical waveguides photodiode (MSOWPD) integrated with CMOS/BiCMOSASICs, according to some embodiments. The MSOWPD replaces the MSPD as inFIGS. 58, 59 and 60. Microstructured optical waveguide avalanchephotodiodes (MSOWAPDs) can similarly be fabricated and integrated withthe addition of a charge and multiplication (avalanche) layers/regionsto create a P-P-PN or P-I-P-I-N structure. The cores (e.g. 6212, 6214and 6216) of the MSOWPDs can be connected by first coating the surfacewith the MSOWPD with a polymer such as polyimide that can fill only thetop gaps due to its viscosity and surface tension. After curing, aplasma ashing can be performed to remove the polymer from the surfacebut not in the gaps, exposing the top of the cores. This layer is notshown in FIG. 62A for simplicity. A transparent conducting metal oxidecan be deposited on the top surface to connect the cores and the topsurface electrically such that a reverse bias can be applied to thecores and the top surface anode and cathode. A reverse bias voltage canrange from −1 to −5 volts.

As shown in FIG. 62A the structure except for the MSOWPD, is similar toFIGS. 59A and 59B and in some cases a BOX can be included as in FIG. 58.

The microstructure optical waveguide (MSOW) can be etched partially intothe I or low doped region and/or though the I or low doped region and insome cases to the N⁺⁺ doped region and in some cases pass the N⁺ dopedregion. The lateral dimension of the MSOW which can consist of amicrostructured hole and one or more microstructure cores, can rangefrom 500 nm to 8000 nm and the core lateral dimension can range from 300nm to 7500 nm and spacing between the MSOW can range from 50 nm to 5000nm.

The MSOW core shape can be circular, oval, hourglass, square, polygonfor example. The core shape can also be circular, oval, square, orpolygonal. The cores can be uniformly space and/or not uniformly spaces.The MSOW can be periodic and/or aperiodic.

The dimension of the MSOWs range from sub wavelength to 10 wavelengthand can have photon trapping properties, slow wave effects, that canenhance the absorption of material with weak absorption for wavelengthsat or just shorter than the bandgap wavelength of an indirect bandgapsemiconducting material. Weak absorption can mean at certain wavelengthsof light, the material bulk absorption coefficient is between 10 s to100 s cm⁻¹. In certain cases, when the material is strained the bandgapcan be smaller than the same material that is not strained. Use ofmicrostructure holes and/or waveguides can enhance the absorption ofboth relaxed and non-relaxed semiconductors resulting in higherresponsivity over the same material without microstructure holes and/orwaveguides for absorption enhancements.

Rectangular cross sectional holes are shown in FIG. 62 for the MSOW, theholes can be funnel shaped for example and the core can have a varyingdiameter such as a tapered core for example. Other shapes can includetrapezoidal, and inverted bottle shaped.

FIGS. 62B and 62C are top views showing further aspects ofmicrostructured optical waveguides photodiodes according to someembodiments. As can be seen, different topographies can be provided. InFIG. 62B, rectangular holes are on either side of the middle core 6212s.In FIG. 62C two cores 6214 and 6216 are surrounded by larger rectangularhole.

The MSOWPD/MSOWAPD can also be fabricated in a mesa structure as shownfor example in FIG. 56 with or without a BOX. The optical signal canimpinge from the top surface and in some cases can impinge from thebottom surface through a via.

Data rates of 3-50 Gb/s or higher can be achieved and in some cases datarates from 3-10 Gb/s and in some cases from 20-30 Gb/s and in some casesfrom 25-50 Gb/s or higher. Signal wavelengths as in earlier discussionscan span from 800-1100 nm and in some cases from 800 to 1350 nmdepending on the Ge fraction in GeSi alloy and strain. And in some casesfrom 1250 nm to 1550 nm and in some cases to 2000 nm depending on the Gefraction in the GeSi alloy and strain.

In all the MSPD/MSAPD/MSOWPD/MSOWAPD integration with CMOS/BiCMOS TIA,equalizers, limiting amplifiers and/or other ASICs as necessary, atrench and/or multiple trenches as in FIG. 59B can be included.

See, e.g., Yin et al, Integrated ARROW waveguides with hollow cores, 14Jun. 2004/Vol. 12, No. 12/OPTICS EXPRESS 2710 (incorporated herein byreference); and Litchinitser et al, Antiresonant reflecting photoniccrystal optical waveguides, OPTICS LETTERS/Vol. 27, No. 18/Sep. 15, 2002(incorporated herein by reference and referred to herein as“Litchinitser et al”); In FIG. 1C of Litchinitser et al, a MSOW is shownwith one core in the middle. In contrast, according to embodiments ofthis disclosure, single and/or multiple cores of same or differentdimensions can be provided. In addition, it should be noted that thecores surfaces can be contiguous with the surface surrounding the holesas in FIG. 1C of Litchinitser et al. Where as in the embodiments shownin FIGS. 61A-61D, the cores can also be represented by hole-free areasor regions and in some cases the holes can be photonic crystal.According to embodiments of present disclosure, an MSOW can be avariation of ARROW waveguides with a solid core or cores and apropagation distance in the vertical direction along the waveguide of0.5 to 10 micrometers.

Microstructured photodetectors (MS-PD) can be made polarizationinsensitive or polarization sensitive by the shape and arrangements ofthe microstructure holes. Microstructured holes that are asymmetric indirection tend to be polarization sensitive and microstructure holesthat are symmetric in directions (X-Y) tend to be polarizationinsensitive.

FIGS. 63A-63C are cross section views illustrating aspects of MSPDsintegrated with CMOS/BiCMOS circuitry utilizing selective area growth ofGe and/or GeSi on silicon, according to some embodiments. A siliconwafer is used with epitaxial layer(s) that are compatible withCMOS/BiCMOS fabrication that can also include a BOX (buried oxide)layer. In FIG. 63A, a void 6302 is etched into the N⁻⁻ or P⁻⁻ layer andwhere the top surface and sidewalls can be coated with a dielectric 6308such as silicon oxide, silicon nitride. In FIG. 63B, selective areagrowth of Ge and/or GeSi alloy 6310 with Ge fraction ranging from 0 to100%. The selective area growth of Ge and/or GeSi 6310 can be undopedand/or lightly doped with doping levels less than 5×10¹⁶/cm³ and in somecases less than 3×10¹⁵/cm³ and in some cases less than 3×10¹⁷/cm³.Thicknesses of the Ge and/or GeSi 6310 can range from 300 nm to 5000 nmand in some cases from 500 nm to 2500 nm. The shape of Ge and/or GeSi6310, as viewed from the top, can be circular, rectangular, polygonal,diamond shaped, oval, and/or a combination of those and other shapes. Geand/or GeSi 6310 can have a lateral dimension ranging from 10micrometers to 500 micrometers or more and in some cases from 25micrometers to 100 micrometers. The cross sectional shape can be arectangle (as shown in FIG. 63B), and in some cases can follow thelattice plane of the Si in an anisotropic wet etch and in some cases canbe polygonal and the shape in the two perpendicular lateral directionscan be different. See, e.g., Michel et al, High-performance Ge-on-Siphotodetectors, 30 Jul. 2010| DOI: 10.1038/NPHOTON.2010.157(incorporated herein by reference). According to some embodiments,chemical mechanical polishing (CMP) can be performed after the selectivearea growth to present a smooth flat surface for processing of theCMOS/BiCMOS and photodiode integration.

FIG. 63C shows an MSPD formed on the structure having selective areagrowth of Ge and/or GeSi on silicon. The Ge and/or GeSi 6310 top surfacecan be ion implanted and/or diffused with dopants of P type (can also beN type) to form a P (Ge and/or GeSi)-I(Ge and/or GeSi)-N(Si) structure6384 and can include microstructured holes 6312 etched into the IGe/GeSi 6310 partially and/or entirely using wet and/or dry etching. TheGe and/or GeSi layer 6310 thickness can range from 500 nm to 5000 nm andin some cases 500 nm to 2500 nm for data rate bandwidths of 10 to 50Gb/s or more. Lateral dimension of the photosensitive area for highspeed operation where a high electric field is externally applied via areverse bias between the anode and cathode, can range from 10micrometers to 500 micrometers and in some cases from 25 micrometers to80 micrometers and in some cases from 25 to 100 micrometers

For MSPD, MSAPD, MSOWPD, MSOWAPD, the hole dimension laterally can rangefrom 100 nm to 5000 nm and in some cases from 350 nm to 2500 nm andspacing with adjacent holes can range from 50 nm to 5000 nm and in casescan range from 100 nm to 2000 nm and can be periodic and/or aperiodicand/or combination of periodic and aperiodic. The hole cross sectionscan be any combination of cross sectional shapes including funnel,inverted pyramid, cylindrical, trapezoidal, hourglass, ball shaped,rectangular, and polygonal. The surface shape of the holes can becircular, oval, hourglass, rectangular, polygon, amoeba, or combinationsthereof. The holes can be periodic and/or aperiodic. Etch depth of theholes can range from 100 nm to 10000 nm and in some cases can partiallyetch into the top doped layer, and/or partially into the I layer orlightly doped layer and/or fully through the I or lightly doped layerand/or partially into the lower doped layer and/or through the lowerdoped layer. In some cases the microstructured holes can extend into thesilicon regions vertically and/or laterally.

Operating wavelength can range from 800 nm to 2000 nm depending on theGe fraction in the GeSi alloy. In some cases from 1250 nm to 1350 nm,and in some cases from 1550 nm to 1650 nm. In some cases from 840 nm to960 nm and in some cases from 900 nm to 1070 nm and in some cases from840 nm to 1100 nm and in some cases from 900 nm to 1350 nm. Responsivitycan range from 0.1 A/W to 1 A/W at at least one of the wavelength in thewavelength span. In some cases responsivity can be 0.1 A/W or greater atat least one wavelength in the wavelength span, in some cases 0.3 A/W orgreater at at least one wavelength in the wavelength span, in some cases0.5 A/W or greater at at least one wavelength in the wavelength span, insome cases 0.8 A/W or greater at at least one wavelength in thewavelength span, and in some cases 1 A/W or greater at at least onewavelength in the wavelength span.

Data rates can range from 10-50 Gb/s or higher, in some cases 25 Gb/s orhigher, in some cases 40 Gb/s or higher, and in some cases 50 Gb/s orhigher.

Analog Devices, Inc. data sheet ADN3010-11 11.3 Gbps Optical Receiver(incorporated herein by reference), shows the integration of a SiGe PINphotodiode with TIA and LA with data rate bandwidth to 11.3 Gb/s. Thebandwidth can be limited by the thickness of the SiGe layer which waschosen to achieve a responsivity of 1 A/W. This requires a thicknessranging from 3-4 micrometers with a saturation velocity of approximately0.7×10⁷ cm/s for electrons in Ge. The data rate is thus limited toapproximately 9 GHz or less or approximately 10-13 Gb/s. According tosome embodiments, to achieve higher data rates a thinner GeSi layer canbe provided, and to achieve high responsivity, microstructured holes canbe provided to enhance the absorption and therefore the quantumefficiency and responsivity of a thinner GeSi layer. For example, a 2micrometer or less thick Ge layer can achieve in excess of 22 Gb/s datarate bandwidth and microstructured holes can enhance the absorption ofthinner Ge and/or GeSi layers to improve the responsivity and thereforethe system sensitivity.

In FIG. 63C, shallow P⁺ well 6384 can be implanted and/or diffused intothe surface of the Ge/GeSi 6310 to a depth ranging from 50 nm to 300 nmand with resistivity less than 0.01 ohm-cm and in some cases a thinmetal and/or transparent conducting metal oxide layer (not shown) can bedeposited on the Ge/GeSi prior to microstructure hole etch withthicknesses ranging from 1 nm to 300 nm. Buried N⁺ region 6304 can beformed using selective area ion implantation and/or diffusion, and/orepitaxially grown with resistivity of 0.01 ohm-cm or less and in somecases 0.001 ohm-cm or less and with thicknesses ranging from 100 nm to500 nm or more, on N or P substrate. A buried O and/or N ion implant atselective areas 6334 can be implemented on the N or P substrate prior toN⁻⁻ (or P⁻⁻) or undoped or intrinsic epitaxial growth of 0.5 to 5microns with resisitivity of 1 ohm-cm or greater and in some cases 10ohm-cm or greater. In some cases a SOI substrate can be use.

N⁺ connecting wells 6306 can be formed to connect the cathode to theburied N⁺ layer 6304. The connecting wells 6306 can be post-like withthe post around the perimeter of the photosensitive region defined bythe P⁺ doped layer 6384 and/or a continuous wall around the perimeter.The posts and/or walls can be approximately 2 times the depletion width,for example if the depletion width between the P⁺-I-N⁺ is 2 microns,then the post and/or wall can be 4 microns or more distance from the P⁺region. Cathode metallization is formed on the N⁺ well 6306 and can bering shaped for circular shaped photosensitive areas and anodemetallization can be formed on the P⁺ region 6384. The anode can also bein the shape of a ring for a circular shaped photosensitive region (orit can be other shapes such as a polygonal). Transmission lines (notshown) connect the anode and cathode to the TIA and ASICs. CMOS/BiCMOSTIA and other ASICs can be fabricated on the low doped layer and otherlayer(s) may be provided if Ge/GeSi transistors are used and which arenot shown in for simplicity. Electrical and/or optical isolationtrench(es) 6360 can surround the entire MS-photodetector and in somecases partially surround the MS-photodetector. Many details are notshown, such as passivation, planarization, connecting metals, dielectriclayers, antireflections, backside ohmic metallization if necessary,shallow trenches, and TSVs for solder bumps, for simplicity and clarity.

FIG. 64 is a cross section view showing aspects of aMSPD/MSAPD/MSOWPD/MSOWAPD having surface microstructures and ismonolithically integrated with CMOS and/or BiCMOS ICs, according to someembodiments. The CMOS and/or BiCMOS ICs can include: TIAs, equalizers,limiting amplifiers, clock data recovery ICs, and other ASICs foroptical data communication. In this example, microstructures are shownfor both on top of the semiconductor surface and/or etched into thesemiconductor surface. The microstructures 6414 on top of the surfacecan be a continuation of the semiconductor material above thephotodetectors and/or deposited separately. The upper microstructures6414 can also be a non-semiconductor material such as dielectric,amorphous semiconductor, metal, a combination thereof, or a combinationof semiconductor, non-semiconductor and/or other materials such astransparent conducting metal oxides. The above the surfacemicrostructures 6414 can reduce reflection, and/or channel trappedphotons to the photodetecting region and/or supplement themicrostructures 6412 etched into the semiconductor to further enhancethe absorption. The above surface microstructures 6414 can have anycross sectional shape, for example funnel, inverted pyramids,cylindrical, trapezoidal, V shaped, hourglass, ball shaped and/or acombination of shapes. The lateral shapes of microstructures 6414 can begrating-like, circular, rectangular, polygon, oval, hourglass, amoebashaped, star shaped, chevron shaped, or combination of shape and sizes.The lateral dimensions of microstructures 6414 can range from 20-10000nm and the thickness can range from 10-10000 nm. The spacing ofmicrostructures 6414 can range from 10-5000 nm and can be periodicand/or aperiodic.

The monolithic integrated microstructure enhanced photodetectors andCMOS/BiCMOS electronics may not need further hermetic packaging sincethe entire chip can be passivated with native oxides and/or dielectrics.However in some cases the entire monolithically integrated MSPD/AMSPDwith CMOS and/or BiCMOS electronics chip can be entirely and/orpartially hermetically sealed with dielectrics such as silicon oxide,silicon nitride, aluminum oxide, aluminum nitride, polymers such aspolyimide, and/or spin-on-glass.

Yashiki et al, 5 mW/Gbps hybrid-integrated Si-photonics-based opticalI/O cores and their 25-Gbps/ch error-free operation with over 300-m MMF,OFC 2015 © OSA 2015 (incorporated herein by reference and referred toherein as “Yashiki”) shows a hybrid packaging of photodetector with TIAusing a glass and silicon platform. In contrast, according to someembodiments of this disclosure, a MSPD is monolithically integrated withCMOS/BiCMOS ASICs, which can reduce the entire 25 Gb/s optical receiverto a single chip. The single chip can include TSVs (through siliconvias) that can provide a hollow optical waveguide to theMSPD/MSAPD/MSOWPD/MSOWAPD. According to some embodiments, glass may beused to provide a TGV (through glass via) hollow optical waveguide tothe MSPD/MSAPD/MSOWPD/MSOWAPD.

Also shown in FIG. 64, ion implanting and/or diffusion with dopants of Ptype (N type) can be used to form a P⁺ layer/region 6384. Also, N⁺connecting wells 6406 can be formed to connect the cathode to a buriedN⁺ layer 6404. These structures can be formed according the descriptionsof similar structures shown herein (e.g. FIG. 63C).

FIGS. 65, 66 and 67 are cross sectional views showing aspects ofmonolithically integrated MSPDs and CMOS/BiCMOS ICs with a throughsilicon via (TSV), according to some embodiments. As used herein theterms MSPD/MSAPD/MSOWPD/MSOWAPD collectively can also be referred to asMicrostructured Photodetector, MS-PD, or MSPD. FIG. 65 shows amonolithically integrated MSPD such as one shown in FIG. 58 with an MSPD6510 integrated with CMOS/BiCMOS circuitry 6502 on a silicon substrate.The CMOS/BiCMOS circuitry 6502 be ASICs with TIAs that also includeequalizers, limiting amplifiers, clock data recovery, buffers, and/orelectrical signal transmitters. In FIG. 65 a TSV 6530 is etched throughthe silicon substrate, which can range in thickness from 300 to 1000micrometers. The sidewalls of TSV 6530 can be coated with metal and/ordielectrics to assist in guiding the optical signal to the MSPD. A BOXlayer 6508 can be used as an etch stop layer for the TSV etchingprocess. In some cases the optical fiber 6562, which can be single modefiber (SMF) and/or multimode fiber (MMF), is inserted partially into theTSV 6530. The monolithically integrated MSPD 6510 with CMOS and/orBiCMOS ASICs 6502 can be in the form of a single chip and can be solderbumped directly onto a printed circuit board in a flip chip manner. Thissignificantly simplifies packaging when compared to FIG. 1 of Yashiki.The simplification can reduce the cost of the optical receiver by 25% ormore.

FIG. 66 show a integrated structure as in FIGS. 58-64, with the additionof a TSVs 6690 to provide electrical contacts between the CMOS/BiCMOSelectronics 6602 to the printed circuit board with the aid of solderbumps that both fix the chip in place and provide electricalconnectivity to external circuits. A glass and/or polymer superstratecan be attached to the monolithically integrated chip to provide a lightguide to the MSPD 6610 and can also provide an encapsulation for thechip to seal the chip against the environment. An example of such asuperstrate is discussed in Yashiki.

In some cases, the glass and/or polymer superstrate may be attached atwafer level to simplify packaging and in some cases the glass and/orpolymer superstrate may be 3D (dimension) printed at wafer level. Athrough glass via (TGV) 6630 is provided that may be coated with metaland/or dielectric to provide light guiding with minimal loss and in somecases SMF and/or MMF 6662 can be partially inserted into the TGV 6630.

FIG. 67 is similar to FIG. 66, except showing a 45 degree bend in alight pipe 6730 which allows SMF and/or MMF 6662 to be inserted and/orcoupled to, parallel to the plane of the chip which in some cases may bedesirable. The light pipe 6730 is a hollow optical waveguide that can becoated with metal and/or dielectric layers. In some cases, thesuperstrate can be glass and/or polymer and can be applied at the waferlevel for example and in some cases can be 3D printed at the waferlevel. See, e.g., Pyo et al, 3D Printed Nanophotonic Waveguides,http://onlinelibrary.wiley.com/doi/10.1002/adom.201600220/abstract(incorporated herein by reference). In some cases, the optical waveguide6730 can be made of semiconductor. See, e.g., Miura et al, Modeling andFabrication of Hollow Optical Waveguide for Photonic IntegratedCircuits, Jpn. J. Appl. Phys. Vol. 41 (2002) pp. 4785-4789 (incorporatedherein by reference).

FIG. 68A is a cross section showing a layer structure of Ge and/or GeSion Si for monolithic integration of an MSPD with CMOS/BiCMOS ASICs,according to some embodiments. The Ge and/or GeSi layer 6802 is lowdoped and/or not intentionally doped layer with resistivity in theneighborhood of 1-10 ohm-cm or higher. N⁺⁺ and/or P⁺⁺ layer(s) can alsobe included on opposite sides of the Ge and/or GeSi layer 6802. Layer6804 is one such layer, and another layer (not shown) could be diffusedor grown on top of layer 6802. The doped layers can have a resistivityin the neighborhood of 0.005-0.001 ohm-cm or lower and thickness canrange for the doped layers from 50 nm to 500 nm and in some cases from100 nm to 300 nm. The N⁺ (or P⁺) doped layer 6804 can be buried byselective area ion implantation and/or diffusion of N type dopants inthe N⁻⁻ or P⁻⁻ I Si layer, in some cases, the N⁺ layer 6804 can beepitaxially grown on the I Si layer 6806 and in some cases the N⁺ layer6804 can be selectively etched away in areas where the CMOS/BiCMOSTIA/ASICs will be fabricated together with the Ge/GeSi layer 6802. Insome cases, the ion implant and/or diffusion can be a blanket areaimplant instead of selective area and the doped region can be etched offprior to CMOS/BiCMOS processing. Ge/GeSi can be grown on the buried N⁺layer 6804 which is in and/or on top of the low doped Si layer 6806 asshown in FIG. 68A.

The undoped or low doped layer 6802 can range from 500 nm to 5000 nm andin some cases from 500 nm to 2000 nm. The Ge fraction in the GeSi alloycan range from 0.1% to 100%, where 100% is all Ge. The Ge and/or GeSilayer 6802 can be grown on a Si layer 6806 that can have a resistivityin the neighborhood of 1-30 ohm-cm or more and a thickness ranging from0.5 to 2 microns and in some cases approximately 1.1 microns. In somecases the Ge and/or GeSi layer 6802 can be grown on other layer(s) thatmay be needed for CMOS/BiCMOS electronics, which can include circuitryfor: signal processing; conditioning; enhancements; storage; buffering;transmission; and other processes for specific applications such as datacenters, high performance computing, and LIDAR. The thicknesses of theGe/GeSi layer for MSPD may be determined for desired specificapplications, bandwidths, responsivity, voltages, for high bandwidthdata rate optical communications for datacenters and/or for highsensitivity lower data rate bandwidth for LIDAR for example. Germaniumresistivity verses doping is given byhttp://www.ioffe.ru/SVA/NSM/Semicond/Ge/electric.html (incorporatedherein by reference).

FIG. 68B is a cross section showing some further aspects of amonolithically integrated CMOS/BiCMOS ASICs with a MSPD using a Geand/or GeSi on Si, according to some embodiments. For simplicity conicalcross sectional holes 6812 are shown which can also be invertedpyramids, funnels, cylindrical, hourglass, microstructured opticalwaveguides and/or any combinations thereof for example. Lateraldimensions of the microstructures holes and/or waveguides can range from100 nm to 5000 nm and in some cases from 300 nm to 2500 nm, spacingsbetween adjacent holes, waveguides can range from 50 nm to 2500 nm andin some cases from 100 nm to 1000 nm. Microstructure holes 6812 can beperiodic and/or aperiodic and any combination of periodic and aperiodic.Vertical depth of the holes and/or waveguides can range from 100 nm to5000 nm and in some cases from 300 nm to 2000 nm. The microstructuredholes/waveguides 6812 can be etched pass the first doped layer 6884 onthe surface, and/or into the low doped or undoped region 6802 and insome cases can be etched to the second doped layer 6804 and in somecases can be etched past the second doped layer 6804.

FIG. 68B also shows a bottom N⁺⁺ doped layer 6804 that can either beepitaxially grown on the I or low doped Si layer and/or it can be formedby selective area ion implantation and/or diffusion of N type dopants.The N⁺⁺ (or P⁺⁺) region 6804 can be formed in the silicon I or low dopelayer prior to Ge and/or GeSi layer growth. A P⁺⁺ shallow well 6884 canbe formed partially on the Ge and/or GeSi surface and on which an anodemetallization and electrodes can be formed. A mesa etch to the N⁺⁺region and the N⁺⁺ region, cathode metallization and electrodes can beformed to compete a P-I-N microstructure photodiode and/ormicrostructure avalanche photodiode with the addition of a charge andmultiplication (avalanche) layers. Passivations are not shown and can bethe same as Kang et al 2008 for example. The CMOS/BiCMOS integratedcircuits are formed first by etching the Ge and/or GeSi away, and insome cases the etching may not be performed if CMOS and/or BiCMOS areformed on the GeSi. An electrical isolation trench (not shown) isoptional. The optional trench can also provide optical isolation. A BOXlayer can be included. A reverse bias voltage is applied between theanode and cathode and the high speed electrical signal is extracted fromthe anode and cathode via a transmission line that is connected to theinputs of electronics such as a transimpedance amplifier (TIA) and/orequalizer and/or other ASICs. Wavelength range can span from 800 nm to2000 nm and in some cases to 2100 nm or longer if the Ge is not relaxed,and in some cases from 800 nm to 1100 nm, in some cases from 1250 nm to1350 nm, in some cases from 1250 nm to 1550 nm, in some case from 1000nm to 1650 nm, in some cases from 900 nm to 1700 nm, and in some casesfrom 900 nm to 1350 nm. Data bandwidth for a single channel can be 5Gb/s, 10 Gb/s, 25 Gb/s, 30 Gb/s, 40 Gb/s, 40 and/or 50 Gb/s, 80 Gb/s,100 Gb/s or higher at the output of the electronics of themonolithically integrated chip at at least part of the wavelengthsdescribed above depending on the Ge fraction in the GeSi alloy.Responsivity can be 0.1 A/W or higher at at least part of the wavelengthspectrum, in some cases can be 0.3 A/W or higher, in some case can be0.5 A/W or higher and in some case can be 0.8 A/W or higher. Usingamplification by avalanching process, the responsivity can be higher by3 dB, 6 dB, 9 dB and/or 12 dB, respectively.

Optical signals can impinge from the top surface as shown. The lateraldimension of the microstructure photodetector (MSPD, MSAPD, MSOWPD,MSOWAPD) can range from 20 to 500 micrometers. In some cases themicrostructured (MS) photodetector is circular, and the diameter canrange from 20 to 500 micrometers or more and in some cases from 30 to 80micrometers. The MS photodetector can also be illuminated from thebottom through a via (not shown). TSV(s) can be used to solder bump themonolithically integrated chip to the printer circuit board either fromthe front or from the back as shown for example in FIGS. 65-67.Passivation and/or encapsulation can be used to avoid the use ofhermetic packaging.

The MSPD's large photosensitive area can be used for both single modefiber and multimode fiber. Since the photosensitive area is large, thealignment of the optical fiber can be passively aligned with alignmenttolerances of many micrometers and in some cases 10 or more micrometerswhich can greatly reduce the cost of packaging. For comparison, withwaveguide type detectors having dimensions of a few microns, single modefiber alignment can have alignment tolerances less than a micrometer.Such tolerances are sometimes achieved using active alignment techniqueswhere a fiber light is transmitted into the fiber during coupling to thewaveguide photodiode while the output of the photodiode is monitored.This active alignment can represent a significant portion of thepackaging cost.

In addition, the monolithic integration of MSPDs with CMOS/BiCMOS ASICscan be single MSPD and/or multiple such as 4 MSPDs connected toCMOS/BiCMOS ASICs. In some cases 8, 16, 32 or more MSPDs can beintegrated for parallel optical and/or coarse wavelength divisionmultiplexing (CWDM). In addition, for LIDAR applications, the lateraldimension of the MSPD/MSAPD can be 1000 microns and can be a square,rectangular or polygonal shaped MS-photodetector to provide highsensitivity at low revers bias voltages in the range of −10 to −35V. Theuse of MS-holes allow the use of thin layers and therefore lowervoltages. Commercial Si APDs can have a reverse bias voltage as high as−100 volts for example.

FIGS. 69A and 69B are cross section views showing some aspects ofmonolithic integration of a MSPD with CMOS/BiCMOS ASICs, according tosome embodiments. Note that some necessary CMOS/BiCMOS layers may not beshown for simplicity. A BOX layer can be included followed by a dopedlayer 6904 such as N⁺⁺ (or P⁺⁺) implanted and/or diffused into thedevice layer of the SOI and/or grown on the device layer epitaxiallywith resistivity in the neighborhood of 0.01 ohm-cm or less and in somecases 0.001 ohm-cm or less. A low doped or undoped layer 6902 of Siand/or GeSi can be formed with resistivity in the neighborhood of 1-30ohm-cm or more. Further layers used for the CMOS/BiCMOS ICs are notshown. Thickness of the low doped and/or undoped N⁻⁻ (P⁻⁻) layer 6902can range from 0.5 to 5 micrometers and in some cases from 0.5 to 2micrometers. The doped layer 6904 thickness can range from 0.1 to 0.5micrometers. The BOX layer, if included, can range from 0.2 to 4micrometers or more. A device layer (not shown) can be formed betweenthe BOX and layer 6904, that can range from 0.1 to 0.3 micrometers. Ahandle wafer and/or silicon substrate can range from 400 to 1000micrometers.

The highly doped layer 6904 may be gown and/or implanted and/or diffusedprior to the low doped and/or undoped layer of Si and/or GeSi 6902 wherethe Ge fraction is less than 100% and in some cases less than 50% and insome cases less than 40% and in some cases can be relaxed and/or notrelaxed. Shown in FIG. 69B, a N⁺⁺ connecting well 6906 can be diffusedand/or implanted to make contact with the doped layer N⁺⁺ (or P⁺⁺) 6904and cathode metallization such as an ohmic contact and metal electrodesare formed on the doped N⁺⁺ connecting well 6906 which can have aresistivity of 0.01 ohm-cm or less and in some cases 0.001 ohm-cm orless. A shallow trench can be etched around the photosensitive regiondefined by the P⁺ or P⁺⁺ doped region 6984 on the surface of the Siand/or GeSi, to reduce the distance of the diffusion and/or ionimplantation to the doped N⁺⁺ layer 6904. The doped N⁺⁺ connecting well6906 can form a continuous perimeter around the P⁺⁺ region 6984 and/orthe connecting N⁺⁺ well 6906 can form a few points such as posts that isnon-continuous around the P⁺⁺ region 6984, which can reduce thecontribution of capacitance to the over all P-I-N structure. The P⁺⁺layer 6984 can be formed on part of the surface of the Si and/or GeSiwith a resistivity of 0.01 ohm-cm or less and in some cases 0.001 ohm-cmor less, and with an anode metallization to complete the P-I-N structureand microstructure holes 6912 (or waveguides) can be dry and/or wetetched as discussed in earlier monolithic integrated structures. Themicrostructure holes 6912 can be inverted pyramids, be funnel shaped,and/or have cylindrical, conical, or hourglass cross sections. The holes6912 can be circular, oval, square, polygonal, hourglass, amoeba and/orany combination of shapes. Dimensions, spacings, doping, thicknesses,bandwidths are similar to those discussed earlier such as for exampleFIG. 68B. For example, the lateral dimensions of the microstructuresholes can range from 100 nm to 5000 nm and in some cases from 500 nm to2500 nm. The spacing between adjacent microstructures can range from 50nm to 5000 nm, in some cases from 100 nm to 1500 nm and in some cases 20nm to 2000 nm. The spacing can be periodic, aperiodic ora combination ofperiodic and/or aperiodic. The depth of the microstructure holes canrange from 100 nm to 5000 nm. In some cases the holes can be etched pastthe first doped layer 6984 and partially into the low doped and/orundoped layer 6902, in some cases entirely through the low doped layer6902 and partially into and/or past the second doped layer 6904. In somecases, the first doped layer 6984 can be formed after microstructureholes 6912 are etched partially into the low doped and/or undoped region6902 by selective area ion implantation and/or selective area diffusionof dopants as in FIG. 42. The thickness of the doped layers 6984 and6904 can range from 100 nm to 500 nm with resistivity in theneighborhood of 0.01-0.001 ohm-cm or less. The low doped layer 6902 canhave a thickness ranging from 0.5 to 5 micrometers and in some cases 0.5to 2 micrometers. The low doped layer 6902 can have a resistivity in theneighborhood of 1-100 ohm-cm or higher. Data rates from the output ofthe monolithically integrated MS-photodetector with CMOS/BiCMOS ASICschips can range from 2-50 Gb/s or higher, 10 to 50 Gb/s or higher, 25Gb/s or higher, 30 Gb/s or higher, 40 Gb/s or higher, 50 Gb/s or higher,80 Gb/s or higher, and in some cases 100 Gb/s or higher. Multiple MSPDsand CMOS/BiCMOS ASICs (application specific integrated circuits) can bemonolithically integrated on a single silicon chip that can be solderbumped directly to a printed circuit board. The optical signal can enterfrom the top, the bottom and/or from the side as in FIGS. 65, 66 and 67.Arrays of MSPDs of 4 for example each operating at 25 Gb/s can achievean aggregated bandwidth of 100 Gb/s and if each each MSPD and associatedASICs can operate at 50 Gb/s then the aggregated bandwidth can be 200Gb/s. In some cases an array of 4×2 each at 50 Gb/s can achieve anaggregated bandwidth of 400 Gb/s. A 4×4 array can achieve 800 Gb/s. Thearray can keep increasing to n×m where n and m are whole numbers, andn×m×BW (BW is the output bandwidth od the monolithic chip for eachchannel, where channel can be a single MS-PD with its associated ASICs)will give the aggregated bandwidth. The diameter, assuming a circularphotosensitive area can range from 10 to 500 micrometers, in some cases25 to 100 micrometers and in some cases 30 to 80 micrometers. Thephotosensitive area can have other shapes such as square, polygonal, oroval. The distance between multiple MSPDs is determined by applications.For example in parallel optics, the distance can be as much as 250micrometers, while for other applications, such as imaging or LIDAR, theMSPD can be as closely spaced as a few micrometers. In some applicationsthe spacing may be in a regular and/or irregular patterns,

MSPDs/MSOWPDs can be operated at a reverse bias voltage in the range of−1 to −5 V applied to the anode and cathode, in some cases at −3.3V.MSAPDs/MSOWAPDs can be operated at a reverse bias voltage in the range−5 to −30V applied to the anode and cathode. These ranges can be appliedto monolithically integrated MSPSs/MSAPDs with CMOS/BiCMOS ASICs.described herein, supra.

The wavelength span can range from 800 nm to 1100 nm, in some cases to840 nm to 960 nm, in some cases 940 nm to 1100 nm, in some cases 1100 nmto 1250 nm, in some cases 1250 nm to 1350 nm, in some cases 1350 nm to1550 nm, and in some cases 1550 to 2000 nm. Responsivity can be 0.1 A/Wor higher at at least part of the wavelength span, in some cases 0.2 A/Wor higher, in some cases 0.3 A/W or higher, in some case 0.5 A/W orhigher, in some cases 0.8 A/W or higher at at least part of thewavelength span. For MSAPD and/or MSOWAPD, the gain can range from 2-10or higher, in some cases 2-100 or higher and the responsivity of theMSPD/MSOWPD can be multiplied by the gain factor of 2-10 and/or 2-20 ormore. For example, a MSPD having responsivity of 0.5 NW can correspondto a MSAPD having a responsivity of 5 A/W with a gain of 10. In somecases, the gain times bandwidth product can be a constant, and thehigher the gain the lower the data rate bandwidth. For LIDAR and someLiFi applications, high sensitivity can be a higher priority thanbandwidth in which case a high gain can be desirable and bandwidth canbe in the high Mb/s to low Gb/s. Reverse bias voltage may range in the−20 to −50V. The different wavelength spans depends on the amount of Gein GeSi alloy.

In all the monolithically integrated MSPDs with CMOS/BiCMOS ASICs anelectrical isolation trench (such as trench 6960) may be used to isolatethe MSPD from the electronics. The trench can also isolate stray opticalsignals from interfering with the electronics.

In some cases, in all the monolithically integrated MSPDs withCMOS/BiCMOS electronics, transparent conduction metal oxides,semitransparent metal of a few nm thickness, can be used on the topdoped layer where the holes are etched through to help reduce seriesresistance.

As described herein supra, the optical signal can impinge from the topsurface and a TSV can be used to contact the electrodes to the bottom ofthe substrate such that solder bump can be formed to solder bump themonolithic chip directly to a printed circuit board. The optical signalcan also be illuminated from the back (or bottom) through a via and thefront (or top) side is solder bumped to the printed circuit board. Asdescribed herein supra, a reflective layer can be used on one surface toreflect back any stray optical signal back to the microstructures forfurther enhancement of the absorption and to reduce the thickness of thelow dope or undoped layer further to increase the bandwidth.

In some cases multiple MS-photodetectors are integrated with CMOS/BiCMOSelectronics to increase the aggregated bandwidths to 100 Gb/s, to 200Gb/s, 400 Gb/s, 800 Gb/s, 1200 Gb/s or more. In some cases a densemultiple MS-photodetector with CMOS/BiCMOS can be used for imaging suchas for LIDAR and/or other robotic applications where high data ratesfrom each MSPD maybe a few Gb/s or less but the aggregated rate from theentire array of MSPDs may be high, such as 100 Gb/s or higher.

Microstructured holes and/or waveguides for photon trapping for theenhancement of absorption can be applied to single crystalline, polycrystalline, micro crystalline, and amorphous material, and in somecases to polymers, semimetals, semiconductors, dielectrics, glass, andinsulators. In the case of insulators, dielectrics and glass, thosematerials can be doped with photo active ions such as Yt, Er and otherrare earth elements and F-center, other color centers, for optical gainsuch as for fiber laser, optical disk amplifiers, or holographic imagestorage. Microstructured holes and/or waveguides for photon trapping forthe enhancement of absorption can be applied to the detection of photonsand/or the amplification of photons where the material can have gain forexample, such as optical amplifiers, light emitting diodes and lasers.In the detection of photons, an external reverse bias voltage is appliedbetween the anode and cathode, in the amplification and/or generation ofphotons a forward bias voltage is applied between the anode and cathode.In some cases, such a fiber amplifiers, an optical source provides apump to amplify the optical signal where the microstructure holes can beused to photon trap both the pump source and the optical signal suchthat photon trapping or slowing can enhance their interaction time formore efficient amplification.

FIG. 70A is a cross section illustrating some aspects of integration ofa MSPD with CMOS/BiCMOS ASICs, according to some embodiments. The MSPDcan be a MSAPD, MSOWPD, MSOWAPD, and the ASICs can include TIAs,Equalizers, Limiting Amplifiers, buffers, drivers, other signalprocessing circuitry, data transmission circuitry, and othercomputing/storage components using standard CMOS/BiCMOS processing. On aP⁺ Si wafer with resistivity in the neighborhood of 0.02 ohms-cm orless, a N⁻⁻ layer 7002 is epitaxially grown. The layer 7002 can have athickness of 0.5-2 micrometer, in some cases approximately 1 micrometer,in some cases approximately 2 micrometers, and in some cases 1-5micrometers or more. N⁻⁻ layer 7002 can have resistivity in theneighborhood of 1-30 ohm-cm or more and in some cases 10 ohm-cm orhigher. CMOS/BiCMOS ASICs are formed. In some cases additional layerssuch as GeSi may be provided for the CMOS/BiCMOS components. The N⁺⁺shallow well 7084 can be formed on part of the surface and the N⁺⁺defines approximately the area of photosensitivity for high speed and/orhigh sensitivity applications. The cathode is formed on the well 7084.The N⁺⁺ well 7084 can be diffused and/or ion implanted with N type ionsto a depth ranging from 100 nm to 300 nm and with resistivity in theneighborhood of 0.01-0.001 ohm-cm or less. A multiple energy ionimplantation process can be used to for a more uniform distribution ofimplanted ions. The P⁺⁺ connecting well 7006 to the P⁺ substrate can beformed and where the anode metallization can be formed on the P⁺⁺ well.In some cases the P⁺⁺ connecting well 7006 may not be needed since theanode for the MSPD can be formed on the bottom of the P substrate suchas shown in FIG. 70A. In some cases a metal connecting electrode can beformed from the surface to the P⁺ substrate via a trench (not shown) andin some cases a TSV (not shown) can be formed to the bottom anode metal.As described herein supra, the connecting well 7006 can be at a fewspots/posts or it can form a continuous perimeter around thephotosensitive region defined mainly by the region under the N⁺⁺ layer7084 where a high electric field can exist with a reverse bias betweenthe cathode and anode with voltages in the range −1 to −4 volts and insome cases −3.3 volts. Microstructures such as holes 7012 and/orwaveguides can be etched past the first doped layer 7084 and partially(5% to 95% for example) into the low doped and/or undoped region 7002.In some cases the microstructures can be etched pasts the low dopedand/or undoped region 7002 and to the P⁺ (or N⁺) substrate.

Shape, dimensions and spacing of the microstructures are as describedherein supra, and a combination of holes and/or microstructure opticalwaveguides can be provided as in FIG. 61. The lateral dimensions of themicrostructures can range from 100 nm to 3000 nm and in some cases 300nm to 3000 nm. The spacing can range from 50 nm to 3000 nm and can beperiodic, aperiodic and/or a combination of periodic and aperiodic. Thedepth of the microstructures can range from 50 nm to 10000 nm, in somecases 300 nm to 2000 nm and in some cases 300 nm to 5000 nm. The crosssectional shape of the microstructure holes can be funnel as shown,inverted pyramid, cylindrical, polygonal, ball like, oval, hourglass,conical, and/or any combination of shapes with multiple sidewall anglesachieved by a combination of dry etchings and/or wet etchings. Themicrostructures can be passivated with native thermal oxide, amorphoussemiconductor, dielectric, cryalline semiconductor, micro and/or polycrystalline semiconductor, polymer, and/or any combination ofpassivations physical, chemical, hermetic and/or non hermetic sealingand/or packaging. Antireflection using dielectric, dielectric stacks,nanostructures, microstructures can be used to reduce reflection. Inaddition the CMOS/BiCMOS ASICs can be covered with a light shield tominimize interference. An electrical and/or optical isolation trench7060 may be etched for further electrical and/or optical isolation. Asin earlier discussions the integrated MSPD(s) with CMOS/BiCMOS ASICs canbe solder bumped either on the front and/or back surface withappropriate paths for the optical signal to reach the MSPD.

Not shown for simplicity are the CMOS/BiCMOS structures and interconnectmetals to form the ASICs nor the electrodes connecting the MS-PD to theASICs.

Depending on the Ge fraction in the GeSi, the wavelength can span from800 nm to 1600 nm, in some cases from 840 nm to 1100 nm, in some casesfrom 1250 nm to 1350 nm, in some cases 1500 nm to 1600 nm, in some cases800 nm to 2000 nm, in some cases 800 nm to 880 nm, and in some cases1000 nm to 1350 nm. Responsivity can be 100 mA/W or higher at at least afew wavelengths in the span, in some cases can be 200 mA/W or higher atat least a few wavelength in one of the wavelength spans, in some cases300 mA/W or higher at at least a few wavelengths in one of thewavelength spans, in some cases 400 mA/W or higher at at least a fewwavelengths in one of the wavelength spans, in some cases 500 mA/W orhigher at at least a few wavelengths in one of the wavelength spans, insome cases 600 mA/W or higher at at least a few wavelengths in one ofthe wavelength spans, and in some cases 700 mA/W or higher at at least afew wavelengths in one of the wavelength spans. Data rate bandwidth fromthe integrated MSPD(s) and ASICs can range from 10 to 100 Gb/s or higherfor a single MS-PD-ASICs integration, in some cases 25 Gb/s, in somecases 30 Gb/s, in some cases 40 Gb/s, in some cases 50 Gb/s, in somecases 80 Gb/s and in some cases 100 Gb/s. In a quad configuration where4 MSPDs are integrated with ASICs, data rate from the integrated chipcan be quadrupled to 40-400 Gb/s. With higher number of MSPDs in thearray, the data rate can be further increased, approaching 1000 Gb/s ormore.

For some applications such as LI DAR, where high data rate is lessimportant, high sensitivity is more important and an MSAPD and/orMSOWAPD can improve system sensitivity significantly, a low voltage APDis desirable for integration with CMOS/BiCMOS. Using microstructures,the layer thicknesses can be reduced without sacrificing quantumefficiency and therefore the MSAPD and/or MSOWAPD can be operated atvoltages less than −30V, in some cases less than −25 V, in some casesless than −20V, in some cases less than −15V, and in some cases lessthan −10V. Gain for the MSAPD can range from 2-10 and in some cases2-100. The responsivity of the MSAPD/MSOWAPD can be 10× that of aMSPD/MSOWPD, and can be 20× or more than that of the MSPD/MSOWPD. Forexample, if the MSPD/MSOWPD responsivity is 0.3 A/W and a MSAPD/MSOWAPDwith 20× results in responsivity being 6 A/W.

FIG. 70B is a plot showing absorption for an MSPD simulated using usingfinite difference time domain analysis (FDTD), according to someembodiments. Note that absorption is directly proportional to QE. Theabsorption is for 0.9 micrometer thick I or low doped region (which canalso be the quantum efficiency). The horizontal axis is wavelength from800 nm to 900 nm. At 850 nm wavelength, the absorption coefficient of Siis 535/cm which results in a 5% absorption without microstructure holes.As shown in FIG. 70B, absorption as high as 37% with microstructuredholes can be achieved with 0.9 micron thick I and/or undoped Si layer.This is an over 7× improvement over a similar structure withoutmicrostructured holes for photon trapping and absorption enhancements.The microstructured holes used in this simulation has a hexagonallattice, funnel cross section, with a diameter of 700 nm, a period of900 nm, and an etched depth of 600 nm. The total thickness from thesurface to the P⁺ substrate is 1.1 microns, referring to the structureof FIG. 70A, the N⁺ surface doped well 7084 is 200 nm thick, the P⁺substrate thickness can range from 500 to 1000 microns.

FIG. 70C is a plot showing a FDTD simulation of the optical field in themicrostructure holes, according to some embodiments. The simulation isfor a 0.9 micron thick I or low doped layer and 0.2 micron N⁺ dopedsurface layer on P⁺ substrate as in FIG. 70B. The holes are squareinverted pyramids using wet etch such as KOH and in a square latticewith a period of 1000 nm. The lateral dimension of the microstructurehole is 900 nm per side. An enhanced absorption of 40%, equivalent to40% quantum efficiency, is simulated which is over 7× a similarstructure without microstructure holes. The wavelength span is 800 nm to900 nm and almost constant 40% across the entire wavelength span.

FIG. 70D is a plot of a data rate bandwidth calculation, according tosome embodiments. Curve 7020 is for the MSPD simulated in FIGS. 70B and70C, and curve 7022 is for similar photodiode without microstructureholes taking into account the transit time and RC time of thephotodiode. The I or low doped layer is assumed to be 0.9 microns andfully depleted with a reverse bias voltage of −2 to −3.3V and with aseries resistance of 50 ohms. The bandwidth is given in GHz and can beconverted to Gb/s by dividing GHz by 0.675 (0.675 is an approximateaverage, depending on the digital signal coding, NRZ—not return to zeroor RZ-return to zero, in some cases it can be 0.5 and in other cases itcan be 0.75 approximately). For example, 24.5 GHz can be 36.3 Gb/s. Ascan be seen from the curves 7022 for a PD without microstructure holesand curve 7020 solid for a MSPD, the data rate bandwidth can besignificantly higher for the same diameter PD. For example at 50 micronsdiameter, a PD without microstructure holes has a −3 dB bandwidth of13.6 GHz where as for the same diameter MSPD the −3 dB bandwidth is 24.5GHz or 1.8 times higher bandwidth.

The MSPD data rate, depending on diameter of the MSPD, can range from72.6 Gb/s to 7.4 Gb/s with a structure such as FIG. 70A (and in somecases FIG. 69B) where the I or low doped layer is 0.9 microns thick. Thematerial can be Si and/or GeSi and applies for wavelengths from 800 nmto 2000 nm depending on the Ge fraction in the GeSi which can range from0 to 1 where 0 is all Si and 1 is Ge.

FIG. 71 is cross section view similar to FIG. 70A with the addition of aBOX (buried oxide) layer. The BOX layer can improve the response of theMSPD by reducing the number of photogenerated carriers outside the highfield region between the top N⁺ layer 7084 and bottom P⁺ layer 7104. Inaddition, the BOX layer can provide a discontinuity in the opticalrefractive index that can reflect optical signal not trapped in themicrostructures in the first pass and reflect the optical signal backtoward the microstructures for further absorption enhancements forimproved quantum efficiencies. In some cases, in place of a BOX (SOI)wafer, a bulk wafer such as in FIG. 70A can be used with selective areaand/or blanket ion implantation of oxygen and/or nitrogen ions into theP⁺ substrate to retard and/or to impede the diffusion of deepphotogenertated carriers from diffusing back to the high field regionthat can cause a slow tail in the impulse response and can degrade thedata rate bandwidth of the MS-photodetector. Doping levels of O and Nions can range from 1E17 to 1E22/cm³ and in some cases, other ions suchas metal ions, isoelectronic ions such as H, He, Ar, Ne may be used toreduce the mobility and lifetime of the photogenerated carriers deep inthe P⁺ substrate.

FIG. 72 is a cross section showing some aspects of a MSAPDmonolithically integrated with CMOS/BiCMOS ICs, according to someembodiments. The structure is similar to that of FIG. 36 except insteadof mesa etching and/or a trench etch to connect N⁺ layer, a connectingN⁺ well 7206 is used and in some cases a trench 7262 can be used betweenthe connecting N⁺ well 7206 and the photosensitive P⁺ region 7284 forelectrical isolation and in some cases such a trench 7262 may not benecessary. If an isolation trench 7262 is used, the etch depth can varyand in some cases it continues to the N⁺ layer/region 7204 and in somecases to the multiplication I layer and in some cases through the Pcharge layer. Such isolation trenches may also be used in MSPDs, MSOWPDsas described elsewhere herein if desirable for improvement in deviceperformance. In addition, an isolation trench 7260 may be used betweenthe MSAPD/MSOWADP and the CMOS/BiCMOS integrated circuits.

With a reverse bias applied between the anode and cathode of theMSAPD/MSOWAPD with voltages ranging from −8 to −35 volts, the gain canrange from greater than 2 to 10 or more, in some cases the gain canrange from 2 to 4, in some cases the gain can range from 2 to 8 or more,in some cases the gain can range from 2 to 20 and in some cases from 2to 100. Gain bandwidth product can range from 20 to 300 Gb/s or more andin some cases 500 Gb/s or more. With gain the quantum efficiency can be50% or greater, in some cases 80% or greater, in some cases 100% orgreater, in some cases 200% or greater and in some cases 500% orgreater. Responsivity can be 0.5 A/W (amperes/watt) or greater, in somecases 1 A/W or greater, in some cases 5 NW or greater and in some cases10 A/w or greater. The responsivity is for some wavelengths in the range800-1600 nm, in some cases 800 nm to 990 nm, in some cases 800 nm to1100 nm, in some cases 900 nm to 1250 nm, in some cases 1250 nm to 1350nm, in some cases from 1300 nm to 1550 nm, in some case 1500 nm to 2000nm and in some cases 1500 nm to 1600 nm depending on the Ge fraction inthe GeSi ally which can range from 0 (all Si) to 1 (all Ge). A shallowP⁺ well 7284 is formed on the surface of the I layer by diffusion of Ptype dopants and/or by ion implantation of P type ions. The P⁺ well 7284completes the P-I-P-I-N MSAPD structure, and can have a thicknessranging from 50 to 500 nm and in some cases 100 nm to 300 nm and canhave a resistivity in the neighborhood of 0.01 to 0.001 ohm-cm or lower.In addition, a thin semitransparent metal layer with thickness rangingfrom 10-100 nm and/or transparent conducting metal oxide (TCMO) such asITO (not shown) with thickness ranging from 1 nm to 500 nm can bedeposited on the P shallow well prior to microstructure hole etch. Theaddition of metal and/or TOMO can assist in reducing the series sheetresistance of the P⁺ shallow well 7284. In some cases, it is desirableto have thin P⁺ shallow wells to reduce the generation of photocarriersin the P⁺ well that can reduce the overall quantum efficiency and/orreduce the data rate bandwidth of the MSAPD due to photogeneratedcarriers in the P⁺ region diffusing to the high field region in the Ilayer that can result in a slow “tail” in the impulse response.

The I or low doped layer Si and/or GeSi (N⁻⁻) can have a thickness rangefrom 0.5 to 5 microns with a resistivity in the range of 1-100 ohm-cmand in some cases 10 ohm-cm or greater. The P charge layer Si or GeSican have a thickness in the range 0.05 to 0.2 microns with a resistivityin the range 0.05 to 0.2 ohm-cm approximately. The multiplication I Sior GeSi layer can have a thickness ranging from 0 nm to 0.5 microns andwith resistivity ranging from 0.5-1 ohm-cm or greater. The N⁺ layer ofSi and/or GeSi can have a thickness range of 0.1-0.5 microns and in somecases 0.1 to 0.3 microns and with a resistivity in the range of 0.005ohm-cm or less. The N or P Si device layer can be approximately 0.1 to0.2 microns thick. The BOX layer can be a few microns thick on Sisubstrate. In some cases instead of a SOI wafer, a bulk silicon N⁺ waferwithout a BOX can be used. In some cases O, N and other ions can beimplanted into a N⁺ Si wafer prior to the growth of the avalanchephotodiode layers. See, e.g., FIG. 1 of Kang et al 2008, which shows aGe on Si avalanche photodiode. A similar structure can be fabricatedwith microstructured holes and where the holes can be etched through thecontact layer and into the absorption layer partially and/or entirely.In some cases the holes can be etched to the charge layer and in somecases through the multiplication layer and in some cases to the bottomcontact layer. As in Kang et al 2008, passivation can be amorphoussilicon (a-Si) and/or silicon nitride.

Microstructure holes 7212 can be circular, square, rectangular, polygon,star, amoeba, hourglass, dog bone, oval and/or any combination of shapesand the cross-sectional shapes can be inverted pyramids, funnel, taperedholes, conical, trapezoidal, hourglass, and any combination of shapescreated by wet and/or dry etching and/or electrochemical. Lateraldimensions at the surface of the microstructure holes can range from 200nm to 5000 nm, in some cases 300 nm to 3000 nm and in some cases 500 nmto 2500 nm. The microstructured holes can be arranged in a randompattern, a periodic pattern, an aperiodic pattern, or a combination ofthe foregoing. The hole lateral diameter can also be varied in anymanner. The spacing between adjacent microstructure holes can range from20 nm to 3000 nm, in some cases 30 nm to 1000 nm, in some cases 50 nm to1000 nm, in some cases 100 nm to 1000 nm, and in some cases 100 nm to600 nm. The microstructure holes can be etched to depths ranging from 50nm to 5000 nm, in some cases 300 nm to 2000 nm and in some cases 300 nmto 1500 nm. The microstructured holes can be etched first, followed byformation of the P⁺ region 7284 as in FIG. 42. Or the microstructureholes can be etched through the P⁺ region, an any other layers such athin metal layer 1-20 nm, ITO layer, and/or partially into the I or lowdoped Si and/or GeSi layer. For example the holes can be etched into 10%of the I or low doped layer thickness, in some cases 20% or less, insome cases 30% or less, in some cases 40% or less, in some cases 50% orless, in some cases 60% or less, in some cases 70% or less, in somecases 80% or less, and in some cases 90% or less. In some cases themicrostructure holes can be etched through the I or low doped layer andpartially into the charge layer and/or partially into the multiplicationlayer and/or partially into the N⁺ layer 7204 and/or to the BOX layerand/or if there is no BOX layer, into the N⁺ Si Substrate.

The N⁺ connecting well 7206 connects the cathode metallization with theN⁺ layer 7204 and can be all along the perimeter of the P⁺ regionseparated by 2-10× the depletion distance. For example if the I layer is2 microns then the connecting well can be 4-20 microns or more from theP⁺ region. The connecting well can be a continuous wall and/or postsaround the P⁺ region. In addition in some cases without a BOX theavalanche photodiode layers are grown on a N⁺ substrate of milli-ohm-cmrange (e.g., 1-30 milli-ohm-cm). The cathode can also be formed on thebottom of the wafer and connecting N⁺ wells may or may not be necessarydepending on how the transmission line from the anode and cathode areconnected to the CMOS/BiCMOS ASICs. A TSV may be used to connect thebottom cathode to the electrodes of the ASICs. In some cases surfacecathodes and anodes are preferred for high speed transmission and theconnecting wells are desirable. In certain applications where high datarates may not be necessary, such as LIDAR applications, a bottom cathodemay suffice. An optional light shield 7252 is also shown in FIG. 72.

FIG. 73 is a cross section view of a structure that is similar to thatof FIG. 72 except that a buried N type device layer is included. Theselective area buried ion implant and/or diffusion is made into the Ntype device layer of a SOI can have a thicknesses ranging from 0.2 to0.5 microns with resistivity in the range 1-30 ohm-cm or more. The ionimplanted and/or diffused N⁺ region 7304 can have a resistivity in therange of 6 milli-ohm-cm or less. The multiplication layer and the restof the avalanche photodiode layers can be grown on the buried N⁺ layer7304 and the CMOS/BiCMOS ASICs can be integrated on the I or low dopedlayer and may include extra BiCMOS layers if necessary.

As in FIG. 72, SOI can be replaced with a bulk N⁺ Si substrate andburied O, N and/or other ions into the N⁺ substrate can be implementedto reduce the diffusion of photogenerated carriers in the N⁺ substratefrom diffusion back to the high field regions of the MSAPD.

FIGS. 74 and 75 are perspective views showing some aspects of aconnecting wells for connecting surface electrodes to lower layers,according to some embodiments. The structures as shown in FIG. 73.Although an MSAPD is shown in FIG. 73, the description in FIGS. 74 and75 apply as well to MSPDs. In FIG. 74, well N⁺ 7206 is wall-shaped andconnects the surface cathode 7422 with the bottom N⁺ layer 7304. The P⁺region 7384 is enclosed by the continuous wall of N⁺ connecting well.Ring-shaped cathode metallization 7422 on top the N⁺ connectingwall-shaped well 7206. A ring-shaped anode metallization 7420 is shownnear the perimeter of the P⁺ region 7384. The microstructured holes 7212are etched into the P⁺ region 7384. Shown in dotted outline is theoptional isolation trench 7262. Not shown for simplicity are themonolithically integrated CMOS/BiCMOS ASICs.

FIG. 75 is similar to FIG. 74 except the connecting N⁺ wells are in theform of a series of post-shaped N⁺ wells 7506. The tops of each of N⁺wells 7506 are connected by the ring of cathode metallization 7422encircling the P⁺ region 7384 which has a ring anode metallization 7420.For simplicity, the depth of microstructure holes 7212 is not shown.Also not shown are the integrated CMOS/BiCMOS ASICs. In some cases, forboth the N⁺ connecting wall and the N⁺ connecting posts, the distance tothe P⁺ region 7384 can be less and/or equal to the I layer or low dopedlayer thickness and/or the fully depleted region thickness and in somecases it can be equal to and/or greater than the I layer or low dopedlayer thickness. For example the distance between the connecting well7206 or 7506 to the P⁺7384 (or N⁺ for N-I-P or N-I-P-I-P structures) canrange approximately from 0.5-10× or more of the I layer and/or low dopedlayer thickness.

FIGS. 76A to 76K are diagrams illustrating aspects of a basic processflow for fabricating MSPDs monolithically integrated with CMOS/BiCMOSASICs, according to some embodiments. Note that the focus is on the MSPDprocess flow rather than the well-known ASICs processes flow.

In FIG. 76A shows a simple cross section of a possible CMOS/BiCMOSstarting wafer, with a 1.1 microns N⁻ layer 7602 having resistivity inthe neighborhood of 10 ohm-cm on a P⁺ silicon substrate 7600 withresistivity in the neighborhood of 20 milli ohm-cm. In some cases the N⁻layer 7602 can be 2 microns thick or more. In some cases a SOI wafer(dotted BOX layer) can be used with a P⁺ device layer of thicknessranging from 0.2 to 0.5 microns and resistivity ranging from 10 milliohm-cm to 1 milli ohm-cm or lower. The BOX layer can block thephotogenerated carriers in the substrate from returning to the highfield I region where they could be swept out and could contribute to aslow diffusion “tail” to the impulse response of the MSPD. Such a “tail”could degrade the bandwidth of the monolithic chip (MSPD integrated withASICs). The BOX (buried oxide) layer can also provide a low-refractiveoptical index and can enhance the microstructure holes in higherenhanced absorption. The inverted pyramids microstructure holes (shownin FIG. 76E) have lateral dimension variations from greater than awavelength (900 nm sides and wavelength at 850 nm for example) toapproximately 0 nm at the apex of the inverted pyramid which is muchless than the wavelength. In between the surface lateral dimension andthe apex, there can be a range of lateral dimensions where themicrostructure holes can vary from greater than a wavelength tosubwavelength. In certain regions the microstructured holes of theinverted pyramid can behave similar to a lossy high contrast grating(HCG) when there is a large refractive index difference such as theaddition of a BOX layer. In some cases, front end of line (FEOL)processes can include an ion implantation into the P⁺ silicon substrateto a depth of 0.3 to 0.6 microns or more, and in some cases 0.1 to 0.3microns, of O, N, metal ions, Ar, and/or Xe, with doping ranging from1×10¹⁷ to 1×10²² ions/cm³. The doping reduces lifetime of photogeneratedcarriers, and in some cases P type dopants ions such as C, B, Al, Ga,and/or In ions can be implanted 0.01-0.6 microns or more and in somecases 0.1 nm to 300 nm or more, into the P⁺ substrate. This dopingreduces lifetime of photogenerated carriers in the P⁺ silicon substrate.Similarly for an N⁺ substrate, N type dopant ions such as C, N, P, As,Sb, and/or Bi can be implanted to depths ranging from 0.1 nm to 600 nmor more and with doping concentration ranging from 1×10¹⁷ to 1×10²²ions/cm³ with doping ranging from 1×10¹⁸ to 1×10²² ions/cm³.

FIG. 76B shows a shallow surface well 7684 of N⁺ that can be implantedand/or diffused to a depth of 0.2 microns with a resistivity in theneighborhood of 1 milli ohm-cm and can have a range of 20 milliohm-cm orless. The well width can range from 20-80 microns wide in a circularand/or square and/or polygon shape and in this example is 30 micronswide in a circular shape and in selective area. In some cases a thinlayer of metal such as Pt, Au, Cu, Al, Ni, Cr, V, or Ag can also bedeposited on the N⁺ well of similar diameter and with thickness rangingfrom 1 to 200 nm prior to microstructure hole etch to assist in thereduction of series resistance. In some case transparent conductingmetal oxide can also be use with similar thicknesses.

FIG. 76C is a cross section view adding P⁺ connecting wells 7606 toconnect the surface to the P⁺ substrate 7600. The P⁺ connecting well7606 can ion implanted and/or diffused and can be a ring (as in 7206shown in FIG. 74) and/or posts/columns (as in 7506 shown in FIG. 75). Inthis example well 7606 is ring-shaped/wall-shaped. The P⁺ connectingwell 7606 can have a width ranging from 5 to 50 microns and 1.1 micronsdeep or more and a resistivity in the neighborhood of 10 milli ohm-cm orless and in some cases 1 milli ohm-cm or less. FIG. 76D shows anode 7620and cathode 7622 ohmic metal and metallization on the P⁺ well 7060 andN⁺ region 7684 respectively. In some cases the P⁺ connecting well 7606may not be necessary and the anode 7620 can be formed on bottom of theP⁺ substrate 7600 and a through silicon via (TSV) and/or deep trench canconnect the bottom anode with a surface electrode connecting to theCMOS/BiCMOS ASICs.

FIG. 76E shows the MSPD with inverted pyramid holes 7612 etched usingKOH solutions wet etch on a (100) Si wafer with the squaremicrostructure hole aligned along the wafer flat and the etch is alongthe (111) lattice plane. This wet etch process can be a back end of line(BEOL) process after the bulk of the processing for the CMOS/BiCMOSintegrated circuits are completed. Passivation of the holes can also bea BEOL process. The microstructure holes can be square and can have aside lateral dimension of 900 nm and a period of 1100-1200 nm in asquare lattice. The side wall angle is approximately 54.7 degrees fromthe plane of the surface resulting in an etch depth of approximately 636nm. In some cases the surface lateral dimension can range from 500 nm to2000 nm and the spacing between adjacent microstructure holes can rangefrom 100 nm to 500 nm. In some cases, as mentioned earlier, a BOX layercan be included to further enhance the absorption and therefore thequantum efficiency. FIG. 76F is a top view showing a square lattice ofsquare holes 7612. In some cases, it can be aperiodic and in some casescan be arranged in a random manner with same and/or different holelateral dimensions. In some cases, the microstructure holes can bearranged in a hexagonal lattice. In some cases the microstructure holescan be oriented not parallel to the wafer flat and in some casesdifferent orientations of the wafer such as (111) and (110) can be usedand the microstructure holes may or may not be inverted pyramids. See,e.g., Mavrokefalos et al, Efficient Light Trapping in InvertedNanopyramid Thin Crystalline Silicon Membranes for Solar CellApplications, Nano Lett. 2012, 12, 2792-2796 (incorporated herein byreference and referred to herein as “Mavrokefalos”), which discussesusing inverted pyramids for solar cell applications. In some embodimentsof the present disclosure, an external reverse bias is applied to theanode and cathode for high data rate bandwidth absorption enhancedphotodiode (or avalanche photodiode) and for high sensitivity MSAPD(microstructure avalanche photodiode) with reduced avalanche reversebias voltages for imaging, and LIDAR applications. Improvements inefficiency in Mavrokefalos for a solar cell with inverted nanopyramidsand a solar cell without inverted nanopyramids is about 170% where as insome embodiments of the present disclosure, the improvement in quantumefficiency can range from 500% to 1000% or more for a photodiode withmicrostructure holes as compared with a photodiode withoutmicrostructure holes. In addition solar cells are not biased where asMSPD/MSAPD and other microstructure photodetectors operate at a reversebias with voltages ranging from −1 to −45 volts. In addition, solarcells are not limited by the thickness of the absorption layer since sunlight is a constant source (CW constant wave) and no time is involved,in many cases nanostructured pillar and/or hole solar cells are only afew percent better than a conventional Si solar cell with thickabsorption layers and often times the nanostructured solar cells haveworst efficiency than a conventional solar cell. In some embodiments ofthe present disclosure, the micro/nanostructured hole photodetectorshave time scales ranging from a few picosecond to tens of nanoseconds,data rate bandwidths from 1 Gb/s to over 100 Gb/s and in some cases lessthan 1 Gb/s and in some cases from 25 Gb/s to 100 Gb/s or more. Microand nano structure holes and/or waveguides allow a thinner I or lowdoped layer of Si and/or GeSi to achieve high data rate bandwidth andhigh quantum efficiency at the same time. For example, data ratesgreater than 20 Gb/s and quantum efficiency greater than 50% at 800-850nm wavelength have not being achieved, to the inventors' knowledge,simultaneously in any known silicon photodiode with a usable wavelengthspectrum of 50 nm or more and where the quantum efficiency does not varyby more than 50%, in some cases 30%, in some cases 20%, and in somecases 10% and is not a resonant photodiode where the QE is sharplypeaked. In FIG. 4A of Gao et al, the quantum efficiency (QE)monotonically decrease from 60% at 800 nm to 40% at 900 nm and the datarate bandwidth can be maintained at greater than or equal to 20 Gb/s atall the wavelengths. In some cases nano/microstructure holes can beapplied to GeSi and/or Ge photodiodes and can achieve high data ratebandwidths and high quantum efficiencies with I and/or low doped layersof less than or equal to 2 microns and in some cases 3 microns and insome cases 5 microns at wavelengths where the bulk absorptioncoefficient is weak. For example, in the neighborhood of 1000/cm orless, in some cases 2000/cm or less, in some cases 700/cm or less, andin some cases 500/cm or less, as compared to III-V direct bandgapmaterial which can be 5000-10000/cm or more. Without the usenano/microstructure holes, a thick I and/or low doped layer may be usedto achieve high QE but high data rate bandwidths at the same time cannotbe achieved. In some applications such as for APD, a low avalanchevoltage is desirable and with nano/microstructure holes the avalanchevoltage can be significantly less than a comparable APD without nanomicrostructure holes. A conventional Si APD requires a thick I or lowdoped region which requires a high reverse bias voltage to deplete the Iand/or low doped region before the voltage can be dropped across themultiplication or avalanche region, voltages of −80 to −100 volts arecommon. Whereas with nano and/or microstructure holes APD, the I and/orlow doped region can be thinner by 2 to 10 times or more resulting in alower reverse bias voltage to deplete the I and/or low doped regionbefore the voltage drop across the multiplication or avalanche regionwith reverse bias voltages ranging from −10 to −45 volts approximately.This is also another advantage of using nano and/or microstructure holesfor MSAPD than cannot be achieved with conventional Si and/or GeSiand/or Ge APD. Applications include monolithically integrated MSAPD withCMOS/BiCMOS ASICs for LIDAR and imaging.

In addition, in some cases, the microstructure holes can be verycomplex, as for example in Berenschot et al, Fabrication of 3D fractalstructures using nanoscale anisotropic etching of single crystallinesilicon, J. Micromech. Microeng. 23 (2013) 055024 (10 pp) (incorporatedherein by reference) where the 3D structure can be applied tomicrostructure holes.

FIGS. 76G to 76K are top views showing some aspects of MSPDs/MSAPDs forintegration with CMOS/BiCMOS ASICs on a single silicon chip. In somecases array of MSPD/MSAPD can be integrated with CMOS/BiCMOS ASICs on asingle silicon chip. Only a basic masking and processing steps for theMSPD/MSAPD are shown for simplicity.

FIG. 76G shows the surface N⁺ (can also be P⁺) well 7684 with a diameterranging from 10 to 150 microns and in some cases from 25 to 150 micronsand in some cases 100 to 500 microns or more. The N⁺ surface well 7684defines approximately the N-i-P junction capacitance and also thephotosensitive area for high data rate bandwidth applications. The N⁺well 7684 can be implanted and/or diffused with N type dopants. Othershapes other than circular are also possible, such as square, polygon,triangular, and rectangular. In this example, the N⁺ well 7684 is formedon a N⁻ layer 7602.

FIG. 76H shows a concentric ring of P⁺ connecting well 7606 formedaround the N⁺ surface well 7684. The connecting ring 7606 can have awidth ranging from 1 to 100 microns and can be spaced from the edge ofthe N⁺ well 7684 by 1 (and in some cases less than 1) to 50 times thedepletion depth, if the depletion depth is 1 micron, then in the rangefrom 1 to 50 microns and in some cases 0.5 to 50 microns. The depth ofthe connecting P⁺ well 7606 is to the P⁺ substrate 7600 (shown in FIGS.76A-76E) and in some cases to the P⁺ device layer of a SOI wafer. Insome cases, instead of a concentric ring, the connecting P⁺ (or N⁺) wellcan be a concentric series of posts/columns from the surface to the P⁺layer (as in wells 7506 shown in FIG. 75). The number of post/column canrange from 1 to 20 for example.

FIG. 76I shows N and P ohmic metal and electrode to form the cathode7622 and anode 7620 metallization. The metal can be Al, SiAl, Ti, Pt,and/or Ni, and/or silicides. The width of the metal can range from 1 to50 microns and the metal thicknesses can range from 50 nm to 5000 nm andin some cases to 10000 nm.

FIG. 76J shows coplanar transmission lines 7640 and 7642 attached to theanode and cathode respectively of the MSPD. The transmission lines 7640and 7642 to the CMOS/BiCMOS ASIC 7604. Not shown are also dielectricand/or polymer layers for the cathode coplanar line to cross over theanode contacts and in some cases the anode and the connecting well canhave a gap to allow the coplanar transmission line to cross. In somecases, a dielectric insulating layer may be provided under the coplanartransmission lines.

FIG. 76K shows the square microstructure holes 7612 that are invertedpyramids as a result of wet KOH etch into the silicon. This can be aback end of line (BEOL) process after the completion of the CMOS/BiCMOSASICs. The holes are as described earlier and can be 900 nm to each sideand a period of 1000 nm to 1200 nm in this example and in a squarelattice. Passivations of the microstructure holes and surfaces are notshown for simplicity. The separation of the MSPD/MSAPD to theCMOS/BiCMOS electronics can range from a few microns to 100 s of micronsand in some cases from 10 to 500 microns and in some cases from 5 to1000 microns or more.

FIG. 77A is cross section view of an MSPD, according to someembodiments. The structure shown is similar to FIG. 76A. A 1.1 micron N⁻Si layer 7702 epitaxially grown on a P⁺ Si substrate 7700. In this case,a FEOL (front end of line) CMOS/BiCMOS process is carried out. The P⁺substrate 7700 is first either blanket and/or selective area ionimplanted with a P type dopant ion such as Al, Ga, In that has minimaldiffusion during N⁻ growth for example. B ions may be used if the N⁻layer is grown at a lower temperature. Similarly for an N⁺ Si substrate,N type dopant ions as discussed earlier can be implanted. In thisexample, the P⁺⁺ ion implanted and/or diffused layer 7704 can be on thesurface of the P⁺ substrate 7700 (as shown) or it can be buried beneaththe surface and the depth can range from 0 nm to 600 nm for example, andthe thickness of the layer can range from 10 nm to 1000 nm or more andwith a resistivity ranging from 0.1 to 0.0001 ohm-cm or less. The highdoping levels can reduce the lifetime of photogenerated carriers in thisP⁺⁺ region 7704 to a few ps approximately and in some cases to less thana few hundred ps and/or also to reduce mobility of photogeneratedcarriers. In some cases if the substrate 7700 is highly doped already,the addition of more P type ions (or N type ions for N substrate) maynot be provided. Preventing the diffusion of photogenerated carriersback to the high field I and/or low doped region under a reverse biasvoltage, can reduce the effect of a “tail” in the impulse response ofthe microstructured PD when illuminated with a short pulse optical laserlight. Any energy in the tail can reduce the data rate bandwidth of themicrostructure PD. N⁺ surface well 7784 is also shown. The complete MSPDis not shown, the P⁺ connecting well and the anode and cathode as inFIGS. 76A-E are not shown for simplicity and for FDTD simulationpurposes. The hole size of holes 7712 can range from 600 nm to 2000 nmand the period can range from 900 nm to 3000 nm and can be in a square,and/or hexagonal lattice and/or aperiodic arrangements.

In some cases the N⁻ layer 7702 can be I and/or P-layer with resistivityequal to or greater than 10 ohm-cm approximately and with layerthicknesses ranging from 1 to 2 microns for I, N⁻ or P⁻ layers and insome cases 1-2.5 microns. In some cases the substrate can be N⁺ and insome cases the surface well can be P⁺ and in some cases the FEOL processof diffusion and/or ion implantation into the N⁺ substrate can be Pand/or As ions to a depth ranging from 10 nm to 500 nm and from thesurface ranging from 0 nm to 500 nm or more below the surface.Resistivity of this layer can range from 0.01 to 0.0001 ohm-cm or less.

FIG. 77B is a plot showing a FDTD simulation of the optical fieldspanning wavelengths from 800 nm to 900 nm interacting withmicrostructure holes, according to some embodiments. The holes areinverted pyramid cross sectional shapes in silicon and where theabsorption and therefore the quantum efficiency in the I or low dopedlayer 7702 of 0.9 microns as shown in FIG. 77A as a function of incidentwavelength with the optical signal impinging from the surface where themicrostructure holes are etched. The microstructure holes are etchedwith a KOH solution on (100) silicon plane, along (111) planes resultingin an inverted pyramid with 54.7 degree from the plane of the surface.See e.g., Sato, Basic 2 Anisotropic Wet-etching Lof Silicon:Characterization and Modeling of Changeable Anisotropy,http://gcoe.mech.nagoya-u.ac.jp/basic/pdf/basic-02.pdf (incorporatedherein by reference and referred to herein as “Sato”) which discussesvarious anisotropic etches for silicon, and where KOH is one of theetchants. Passivation with HF dip and/or oxide, dielectric can be usedon the microstructure holes to reduce leakage current. The quantumefficiency can be at and/or just below 40% in the wavelength span of800-900 nm for square microstructure holes with 900 nm and 1200 nm sidesand a square lattice of 1500 nm period. The solid line 7720 is for the900 nm microstructure hole and the dash line 7722 is for the 1200 nmmicrostructure holes. In some cases the QE is 30% or more for certainwavelengths in the wave length range 800-900 nm and in some cases the QEis 20% or more for certain wavelengths in the wavelength range 800-900nm.

FIG. 78 is a cross section view of a structure similar to FIG. 76A witha BOX layer (or on a SOI wafer), according to some embodiments. Thedevice layer 7704 is P⁺ and 0.3 microns thick and the BOX 7708 is about2 microns thick (can have a range from 0.1 to 5 microns or more) and thedevice layer can be ion implanted as in FIG. 77A and/or diffused ordoped during growth to a resistivity in the range from 0.01 to 0.001ohm-cm or less and an I or low doped N⁻ layer 7702 with resistivity of10 ohm-cm or more epitaxially grown and/or wafer bonded on the P⁺ layerto a thickness of 1.1 microns. After the N⁺ layer 7884 is formed, squaremicrostructure holes 7812 are etched using KOH solutions resulting in aninverted pyramid with the side wall (111) plane at a 54.7 angle from theplane of the surface. The side of the microstructure holes 7812 are 900nm in a square lattice with 1200 nm periods. The hole size can rangefrom 600 nm to 2000 nm and the period can range from 900 nm to 3000 nmand can be in a square lattice and/or hexagonal lattice and/or aperiodicand/or random arrangements.

The complete MSPD is not shown, for example the P⁺ connecting well andthe anode and cathode as in FIGS. 76A-C for simplicity and for FDTDsimulation purposes.

FIG. 79 is a plot showing a FDTD simulation of the structure shown inFIG. 78 of the optical field interacting with the microstructure holesin silicon. The absorption of the I or low doped N⁻ layer 7702 is 0.9microns thick (also the quantum efficiency of the MSPD) as a function ofthe optical signal wavelength from 800 nm to 900 nm impinging on the topsurface where the square holes are etched. The solid curve 7920 is forsquare holes with 900 nm sides in a square lattice with a period of 1200nm. The absorption and therefore the QE is mostly above 40% from 800 nmto 900 nm and in certain wavelengths it can be over 50%. In some cases,the QE is 30% or more at certain wavelengths in the range 800-900 nm.And in some cases the QE can be 20% or more at certain wavelengths inthe wavelength range 800-900 nm.

In some cases, KOH may not be allowed in CMOS/BiCMOS fabricationlaboratories due to the possibility of K contamination, in which caseTMAH, EDP and other isotropic and/or anisotropic etchants may be used.See, e.g., Sato; Sato et al, Anisotropic etching rates of single-crystalsilicon for TMAH water solution as a function of crystallographicorientation, Sensors and Actuators, 73(1999) 131-137 (incorporatedherein by reference); Bassous, Fabrication of Novel Three DimensinalMicrostructures by the Anisotropic Etching of (100) and (110) Silicon,IEEE Transactions of Electron Devices, ED-25, 10, 1978 (incorporatedherein by reference). In addition other combinations of wet etchand/orientations, not necessary an inverted pyramid, are possible. Thewet etched and/or dry etched microstructure holes can be any crosssectional shapes and in addition, different cross sections, for exampleperpendicular cross sections can have same and/or different crosssectional shapes. See, e.g., Zubel, Anisotropic etching of silicon insolutions containing tensioactive compounds, Proc. of SPIE Vol. 10175101750L-1 (incorporated herein by reference). In some cases, wet and dryetching can be combined to produce cross sectional shapes that cannot beachieved by either wet or dry etching alone. In some cases wet etch canbe used after dry etch to remove surface damage caused by dry etchingplasmas.

In some applications as mentioned earlier, a superstrate can be attachedwith precision to the monolithically integrated microstructurephotodetector and CMOS/BiCMOS ASICs and in some cases the microstructurephotodetectors can be an array. The superstrate can be precision moldsfrom three dimensional printing with built in bandpass filters andreflectors for CWDM, and/or precision silicon platforms such as MEMSwith or without actuators for movement of mirrors, filters and in somecases the superstrate can be a passive silicon with 45 degree mirroretched to redirect the optical signal that can enter the monolithic chipin plane for example. See, e.g., Hsiao et al, Compact andpassive-alignment 4-channel×2.5-Gbps optical interconnect modules basedon silicon optical benches with 45° micro-reflectors, 21 Dec. 2009/Vol.17, No. 26/OPTICS EXPRESS 24250 (incorporated herein by reference); andRola et al, Triton Surfactant as an Additive to KOH Silicon Etchant,JOURNAL OF MICROELECTROMECHANICAL SYSTEMS, VOL. 22, NO. 6, DECEMBER 2013(incorporated herein by reference). Rola, Anisotropic etching of siliconin KOH+Triton X-100 for 45° micromirror applications, Microsyst Technol(2017) 23:1463-1473 (incorporated herein by reference and referred toherein as “Rola”), in connection with FIG. 1 of Rola an optical fiber iscoupled to a silicon bench mirror etched 45 degree to re direct theoptical beam perpendicular to the fiber.

FIG. 80 is a cross section illustrating some aspects of a MSAPD withmicrostructure holes, according to some embodiments. In this example themicrostructure holes 8012 can be inverted pyramids. In some cases theholes are not inverted pyramids and can be more complex. The holes canbe etched with wet anisotropic and/or isotropic wet and/or dry, and/ordry etching. Not shown for simplicity are the CMOS/BiCMOS ASICs that canbe monolithically integrated with the MSAPD. An electrical isolationtrench 8062 can be etched between the anode 8020 and cathode region 8022as shown in a ring and/or perimeter fashion such that the N⁺ connectingwell 8006 can be isolated from the depletion regions. This isolationtrench 8062 between the anode and cathode can also be applied to earlierdiscussed MSPD with connecting wells to isolate the connecting wellsfrom the depletion regions. In this example of a MSAPD, a SOI wafer isused with a BOX layer 8008 thickness ranging from 0.2 to 4 microns ormore. A device layer (not shown) can be formed between layers 8008 and8004 that has a thickness ranging from 100 nm to 500 nm, and can bediffused and/or ion implanted with N type dopants to a resistivity of0.01 ohm-cm or less. An epitaxial N⁺ layer 8004 can be grown withthicknesses ranging from 200 to 500 nm and with resistivity of 0.01ohm-cm or less. A multiplication or avalanche layer 8026 can then begrown with thickness ranging from 0 to 500 nm that can be intrinsicand/or low doped N and with a resistivity of 0.6 ohm-cm or higher and/or2 ohm-cm for low doped P. A P type charge layer 8028 has a thicknessranging from 50 nm to 200 nm and resistivity in the neighborhood of 0.2to 0.07 ohm-cm. The I and/or low doped N⁻ layer 8002 has thicknessranging from 0.5 to 5 microns and in some cases 0.8 to 2 microns, insome cases 0.8 to 1.2 microns and in some cases 1 microns, and hasresistivity 1-10 ohm-cm or higher (in some cases it can be P− layer withresistivity ranging from 5-10 ohm-cm or higher). A P⁺ well 8084 can bediffused and/or implanted to a depth of 50-300 nm and in some cases 100nm, and in some cases can have a thin layer of metal such as Al, Pt. Cu,Cr, Au, Ag, Ta, V, Zr, W, and/or Fe with thickness ranging from 1 nm to100 nm and/or transparent conducting metal oxide such as indium tinoxide with thickness ranging from 50 nm to 500 nm that can be depositedon the P⁺ surface prior to microstructure hole patterning and etching.Not discussed are thermal anneals for diffusion processes and for ionimplant activation processes and these can be a part of or separate fromthe CMOS/BiCMOS processes. Passivation is not shown for simplicity andclarity. A N⁺ connecting well 8006 can be diffused and/or implanted(multiple energy if necessary) to form a connection for the surfacecathode 8022 to the N⁺ layer 8004. The depth of the well 8006 can be tothe N⁺ layer 8004 and/or past the N⁺ layer. The width of well 8006 canrange from 1 to 30 microns and the resistivity can be 0.1 ohm-cm orless. Cathode ohmic metallization ring 8022 and anode ohmicmetallization ring 8020 can be formed as in FIG. 76I for example. Anelectrical isolation trench 8062 can be etched between the cathode ring8022 and anode ring 8020. The trench 8062 can be formed to a depth ofthe N⁺ layer 8004 for example as shown in FIG. 80. Similarly such anelectrical isolation ring between the cathode and anode can also beetched for MSPD shown in FIG. 76E for example to a depth where itreaches and/or passes the P⁺ layer 8084. In addition, a secondelectrical isolation ring and/or perimeter (not shown) can be etchedoutside the MSAPD and/or the MSPD, and between the MSAPD and/or MSPD,and the CMOS/BiCMOS ASICs if necessary. The width of the rings can rangefrom 100 nm to 1000 nm or more and can be dry and/or wet etched. In somecases, multiple rings for between the anode and cathode and/or betweenthe microstructure photodetectors and the ASICs can be etched to form aBragg reflector to confine the light within the MSAPD/MSPD to furtherenhance absorption and therefore improve the quantum efficiency. Alsonot shown are the transmission lines connecting the anode and cathode tothe ASICs and external power supply that power the ASICs and provide thereverse bias for the MSAPD and MSPD.

As discussed earlier, the microstructure holes 8012 lateral dimensionscan range from 300 nm to 3000 nm or more, in some cases from 500 nm to3000 nm, and in some cases from 600 nm to 2000 nm. The holes can haveany shape, for example, circular, square, rectangle, polygonal, star,amoeba, or fractal. The cross-sectional shape of the holes can beinverted pyramids, fractal, cone, funnel, polygonal, hourglass, amoeba,or continuous curve. Different lattice directions can have differentcross sectional shape, and any combinations of shapes by anisotropic,isotropic and/or dry etching. The spacing of adjacent microstructureholes can vary and/or be constant and can range from 50 nm to 500 nm ormore and can be periodic such as square, hexagonal lattice, aperiodic,random and/or a combination of periodic and aperiodic. In this example,microstructure holes 8012 can be square with each side ranging from900-1200 nm and a period ranging from 1000 nm to 1500 nm in a squarelattice.

The layer thicknesses for the MSAPD is thinner than a conventionalsilicon APD without microstructure holes by a factor of 2 to over 10with similar quantum efficiencies. Thinner layers of the MSAPD canresult in significantly lower reverse bias voltages. For example,instead of −100V in a conventional APD, −45V or less can be achievedwith similar gain, and in some cases −30V or less.

In some cases some or all of the layers, except for the substrate 8000,can be some composition of GeSi where the Ge fraction can vary from 0 to1 for the MSAPD and MSPD.

FIG. 81 is a cross section similar to FIG. 80, and illustrating someaspects of a MSAPD with microstructure holes, according to someembodiments. In this case, instead of a BOX layer a N⁺ silicon substrate8100 is used. A FEOL (front end of line) process of selective and/orblanket ion implantation and/or diffusion of N⁺ type ions into the N⁺substrate 8100 can be performed to form region 8104. The implantationand/or diffusion can be carried out prior to the growth of themultiplication/avalanche layer, charge layer, I or low doped layer. Ptype ions such as Al and/or Ga is attractive due to its larger size thanB and may diffuse less during epitaxial growth. Resistivity of 0.001ohm-cm or less or a dopant density of 1E20 or greater and a thicknessranging from 10 nm to 300 nm or more and with a depth ranging from 0 nmto 300 nm or more, can be desirable to reduce the photogenerated carrierlifetime in these regions away from the high electric field to minimizediffusion of the photogenerated carriers back to the high field regionthat can degrade the high frequency response of the MSAPD. In certainapplications where high bandwidth is not necessary. The BOX and/or highdoping regions may also not be provided and the low avalanche voltage isthe most important factor. Such applications may include LIDAR and imageprocessing. n some cases, some or all of the epitaxial layers can beGeSi with Ge fraction ranging from 0 to 1.

In some cases, the connecting well 8006, connecting the surface cathodeand/or anode to N⁺ and/or P⁺ layers, can be metal for the MSAPD and MSPDand either a ring or post/columns can be used and the number ofpost/columns can range from 1 to 25 or more. Trench isolations asdiscussed earlier may be used for electrical and/or optical isolation.

In some cases, for the highly doped layers, other atoms may be added tocompensate for lattice strain. For example, in highly doped boron layersGe may be added to compensate for lattice strain with approximatelysimilar amount as the doping ions for example.

FIGS. 82A and 82B are cross sectional views of layer structures prior tointegration of a MSPD with CMOS/BiCMOS ASICs, according to someembodiments. Shown are variations of structures shown in FIGS. 77A and78 and prior to microstructure hole etching and connecting wells. Insome cases, the I or N⁻ or P⁻ low doped layers of FIG. 76A, 77A, 78 canhave a thickness ranging from 0.5 to 5 microns and in some cases from 1to 2.5 microns. FIGS. 82A and 82B show further variations of thestarting material for CMOS/BiCMOS integration with MSPD. In FIG. 82A thesubstrate is N⁺8200 and/or the device layer is N⁺ in a SOI. The BOXlayer 8208 can have a range in thickness from 0.1 to 10 microns. FIG.82A is on SOI and the device layer 8204 thickness can range from 100 nmto 500 nm with a resistivity of less than 10 ohm-cm an can be diffusedand/or ion implanted with P and/or As ions to a resistivity of less than0.01 ohm-cm and in some cases less than 0.001 ohm-cm. A P⁺ surface well8284 can be diffused and/or ion implanted with B and/or Al ions to adepth ranging from 10 nm to 500 nm and can include multiple energy ionimplant such that the doping can be uniform to the surface. The width ofthe P⁺⁺ well 8284 can range from 20 to 100 microns and in some casesfrom 25 to 80 microns and in some case from 30 to 500 microns or more.In some cases a thin metal and/or transparent conducting metal oxidelayer can be added on the surface of the P⁺ region with thicknessesranging from 1 nm to 500 nm to reduce series resistance, prior toetching of the microstructure holes. FIG. 82B shows a N⁺ substrate 8216with a FEOL diffusion and/or ion implantation of P and/or As ions to adepth ranging from 10 to 500 nm from the surface of the substrate andcan be 0 nm to 500 nm or more beneath the surface after thermalannealing where the dopants may diffuse. The resistivity of the N⁺⁺layer 8214 can range from 0.01 ohm-cm or less to 0.001 ohm-cm or less to0.0001 ohm-cm or less. In some cases the addition of N⁺⁺ layer may notbe provided if the substrate 8216 is highly doped and/or in some caseswhere the data rate bandwidth degradation due to diffusion current canbe tolerated in certain applications. Not shown in FIGS. 82A and 82B forclarity and simplicity are structures such as the connecting wellsand/or electrodes, the cathode and anodes and its metallization andtransmission lines connecting the MSPD to the ASICs, the microstructureholes which are similar to earlier figures, passivations, antireflectionlayers, planarization effects, and dielectric cross-overs for theelectrodes. Optical signals can impinge from the surface where themicrostructure holes are etched and in some cases the optical signal canimpinge from the bottom where a via can be etched.

In some cases, the monolithically integrated MSPD/MSAPD layer structurescan have one or more GeSi layers with Ge fraction varying from 0 to 1and where the layer(s) can have the same and/or different Ge fractions.This can apply to all earlier discussions and later discussions onmicrostructure photodetectors.

FIG. 83 is a cross section view showing aspects of a starting layerstructure with N⁺ surface well, according to some embodiments. Thestructure is similar to that of FIG. 76B, except with a FEOL (front endof line) ion implant of buried O and/or N ions in the P⁺ substrate 8300.See, e.g., Izumi et al, C.M.O.S. DEVICES FABRICATED ON BURIED SiO2LAYERS FORMED BY

OXYGEN IMPLANTATION INTO SILICON, ELECTRONICS LETTERS 31 Aug. 1978 Vol.14 No. 1 (incorporated herein by reference); Hauthan et al, Improvementin buried silicon nitride silicon-on-insulator structures byfluorine-ion implantation, J. Appl. Phys., Vol. 83, No. 7, 1 Apr. 1998(incorporated herein by reference). The implantation energy can rangefrom 50 to 200 KeV or more and the dose can range from 1E14 to 8E18/cm²(1×10¹⁴ to 8×10¹⁸) or more. B and/or Al can be diffused and/or ionimplanted for a P substrate if necessary above the buried O/N region8314 to from region 8304 having a thickness ranging from 50 to 300 nmand can be 0 to 300 nm below the surface of the P substrate and can havea resistivity of 0.01 ohm-cm or less. For N substrate, P and/or As canbe diffused and/or ion implanted similarly and with a resistivity of0.01 ohm-cm or less. The width of the surface well 8384, N⁺ in thiscase, can range from 20 to 500 microns and in some cases from 25 to 100microns and in some cases 500 to 1000 microns and can be circular,square, or polygonal. Basic processing steps can be similar to FIGS. 76Ato 76F and can include depletion isolation trench ring/perimeter as inFIGS. 80 and 81.

In some cases, the buried O/N implant may not be provided. In some casesthe additional P⁺ and/or N⁺ doping on the P or N substrate 8300 may notbe provided. In some cases both buried O and/or N region 8314 and P⁺ orN⁺ doping on the substrate 8300 can be provided.

The O/N buried ion implant can also applied FEOL to MSAPD for example inFIG. 81 a buried oxygen and/or nitrogen layer can be implanted withsimilar dose as for MSPD followed by P/As diffusion and/or ionimplantation for an N⁺ layer or region. In some cases, one or more ofthe layers can be GeSi with Ge fraction ranging from 0 to 1.

FIGS. 84A and 84B are cross sectional views of a MSPD/MSAPD on SOIand/or a sacrificial layer, according to some embodiments. The structurein FIG. 84A is similar to that of FIG. 71. In this case, the BOX layer8408 is etched away selectively in the region 8490 below themicrostructure holes 8412 and surrounding regions. An etching trench8460 or via is dry etched to the BOX layer 8408 and wet etch can beintroduced through the etch trench to the BOX or sacrificial layer to beetched mostly away and leaving mostly air beneath the microstructureholes. The wet etch for silicon dioxide can be HF based for example. Theetch pattern can be circular and these circular patterns can converge toremove most of the oxide and/or sacrificial layer. In FIG. 84A only theregion under the microstructure holes are shown etched mostly away forsimplicity. However, in practice the region 8490 may extend into alarger region of oxide and/or sacrificial layer extending roughlyequidistance from the etch trench 8460 in all lateral directions withthe etch trench 8460 as the center. In some cases some silicon dioxideand/or sacrificial layer may remain as a spacer layer in the form ofposts, islands and/or regions to provide separation between the bottomdoped layer and the substrate. See, e.g., Judy, Microelectromechanicalsystems (MEMS): fabrication, design and applications, Smart Mater.Struct. 10 (2001) 1115-1134 (incorporated herein by reference); andSmith et al, Embedded Micromechanical DevicesLfor the MonolithicIntegration of MEMS with CMOS, Proc. 1995 IEDM, pp. 609-612(incorporated herein by reference). In some cases, the etch trench/via8460 can be located in the same region as the microstructure holes 8412and in some cases can be located between the cathode and anode and insome cases in region outside the ohmic contact regions.

The removal of the BOX 8408 or sacrificial layer allows higherreflection from the semiconductor-air interface than fromsemiconductor-silicon dioxide interface. This higher reflection, asshown in FIG. 86 infra, can result in an absorption and/or quantumefficiency of greater than 80% for a one micron thick I or low doped Nor P layer of silicon at certain wavelengths in the range of 800 nm to1000 nm. The BOX layer 8408 thickness can range from 0.5 to 10 micronsor more and in some cases less than 0.5 microns. The P⁺ layer 8404 canrange from 100 nm to 500 nm with resistivity of 0.01 ohm-cm or less. TheI or low doped N or P layer 8402 can have a thickness ranging from 0.5to 5 microns and have a resistivity of 1 ohm-cm or more. The N⁺ surfacewell 8484 can have a thickness ranging from 50 nm to 500 nm and in somecases can have a thin metal and/or transparent conduction metal oxidelayer with thickness ranging from 1 nm to 500 nm and the N⁺ well canhave a resistivity of 0.01 ohm-cm or less. The width of the N⁺ well 8484can range from 20-1000 microns and in some cases from 25 to 100 microns,and can be circular, polygonal, star shaped, and/or any combinations ofshapes. The P⁺ connecting wells 8406, in ring/perimeter and/or postform, can be diffused and/or ion implanted to form a connection to theP⁺ layer 8404 and the surface Anode 8420. In some cases, the connectingwell 8406 can be formed by dry and/or wet etching holes to the P⁺ layerand filling with conducting material such as silicide and/or metaland/or high doped amorphous semiconductor. Also shown is an isolationtrench 8462 between the anode and cathode region, which can serve as adepletion isolation trench ring/perimeter to further reduce parasiticcapacitance. In some cases such a depletion isolation ring may not benecessary. In some cases, the depletion isolation ring/perimeter can beetched partially into the I or low doped N or P layer and not entirelyto the P⁺ layer. Not shown nor discussed are passivation, thermalanneals, chemical dips, hermetic sealing if necessary, to reduce surfacedamage and to reduce leakage current.

The microstructure holes 8412 can have cross sectional shapes asinverted pyramids, funnel, cone, cylindrical, hourglass, keyhole,fractal and any combination of shapes that can be created with wetand/or dry etching and in some cases electrochemical etching. Etch depthof holes 8412 as discussed earlier, can be partially into the I or lowdoped N or P layer, partially in the surface doped layer, through the Ior low doped P or N layer, partially into the bottom doped P⁺ or N⁺layer, through the P⁺ or N⁺ layer. In some cases if the microstructureholes are etched to the BOX layer, the silicon dioxide can be etchedmostly away by using the microstructure holes as a conduit for the wetetch to remove the silicon dioxide and an extra etch trench or via maynot be necessary. In some cases, microstructure holes can be etched tothe BOX layer and in some cases can be etched into the BOX layer and insome cases pass the BOX layer and into the Si substrate. Mixtures of HFsolutions in liquid and/or vapor can be used to remove all and/or mostlyall and/or partially the silicon dioxide of the BOX layer and in somecases only dry etching into and/or through the BOX layer is necessaryand HF solutions in liquid and/or vapor may not be used at all. In somecases, the microstructure holes 8412 can be used as a conduit for the HFand/or similar oxide etching solutions in liquid and/or vapor to etchall and/or mostly all and/or partially the silicon dioxide of the BOXlayer. In some cases dry etching alone can be used to remove the BOXlayer partially and/or entirely by etching the BOX layer via themicrostructure holes.

Microstructure hole lateral dimension can range from 300 nm to 3000 nmand in some cases from 100 nm to 5000 nm, and the spacing betweenmicrostructure holes can range from 50 nm to 3000 nm and can be periodicand/or aperiodic and/or any combination of periodic and aperiodic. Themicrostructure holes 8412 can be in a square and/or hexagonal latticeand/or in a random arrangement that can also have lateral dimension ofthe holes varying in a pattern and/or random within certain bounds forexample within 500 to 1500 nm lateral dimension. The microstructure holedimensions lateral and vertical and spacing can be optimize for certainwavelength ranges. The variation can be from subwavelength to about 2×wavelength in free space. For example for 1500-2000 nm wavelength themicrostructure hole range may be 800 nm to 3500 nm. For wavelengthranges from 800 to 1350 nm the microstructure holes can have lateraldimensions from 500 nm to 2500 nm range, In some cases, one or more ofthe layers in FIGS. 84A and 84B can be GeSi with Ge fraction rangingfrom 0 to 1 where 0 is all Si and 1 is all Ge.

In some cases, mesa etching can be used instead of connectingwells/electrodes. A mesa can be etched and passivated with theconnecting electrode in the passivation region and in some cases outsidethe passivation region. See, e.g., FIG. 1 of Kang et al 2008. This canapply to FIG. 84B and all earlier discussions where connectingwells/electrodes were used.

Quantum efficiency can range from 30% to 90% for at least one or morewavelengths in the range of 800 nm to 1000 nm. With GeSi I and/or lowdoped layer, quantum efficiency can range from 30% to 90% for at leastone or more wavelength in the range of 800 nm to 1350 nm, in some casesfrom 1000 nm to 1550 nm, and in some cases from 850 nm to 2000 nm. Notethat quantum efficiency can be directly related to absorption ifcarriers are not lost to recombination and scattering in the I or lowdoped region.

Data rate bandwidth can range from 3 Gb/s to 10 Gb/s, in some cases 10Gb/s to 40 Gb/s, in some cases 25 Gb/s to 50 Gb/s, and in some cases 25Gb/s to 100 Gb/s or higher when monolithically integrated withCMOS/BiCMOS ASICs.

The structure shown in FIG. 84A can also be used for photovoltaicapplication where there is no external bias voltage and used forconverting light to electrical energy. The high efficiency and theinertness of silicon material can be a good candidate for implant underthe skin to power electronics such as heart pacers for example. Inaddition, the structure in FIG. 84A can also be used for energyharvesting of solar energy and convert to electrical energy. Themicrostructure holes allow a greater angle of incidence and canefficiently convert sunlight over a more hours during the daylight thanconventional silicon solar cells.

FIG. 84B is similar to FIG. 80 except for the etch trench or via 8460 asin FIG. 84A to etch mostly away the silicon dioxide layer beneath themicrostructure holes. A depletion isolation trench 8462 can be includedif necessary between the anode and cathode and in some cases thedepletion isolation trench ring/perimeter can be partially etchedthrough the I or low doped layer and/or through the I or low doped layerinto the P charge layer 8428 and/or to the multiplication layer 8426and/or to the N⁺ layer 8424. As mentioned earlier, some silicon dioxidemay be allowed to remain to provide rigidity in the space left void whenthe silicon dioxide is removed. In a mesa can be etched and theconnecting electrode can be outside the mesa area and supported bydielectric and/or poly/amorphous semiconductor that may or may not be apart of the passivation. In addition to the range of thicknesses andresistivity (or doping concentration) given in FIG. 80, the BOX layer8408 can have a thickness ranging from 0.1 to 10 microns or more. The Ndevice layer can have a thickness range of 100 nm to 500 nm and can havea resistivity of 1 ohm-cm or less and can be further doped by N typeions such as P and/or As in a FEOL process with resistivity of 0.01ohm-cm or less, followed by epitaxial growth of N⁺ Si layer withresistivity of 0.01 ohm-cm or less and in some cases 0.001 ohm-cm orless with thickness ranging from 50 nm to 300 nm. A multiplication layerI or low doped N⁻ (or P⁻) 8426 with resistivity of 0.5 ohm-cm or morecan have a thickness ranging from 0 to 600 nm. P charge P layer 8428 canhave resistivity ranging from 0.3 to 0.06 ohm-cm with thickness rangingfrom 50 nm to 250 nm. I and/or low doped N⁻ (or P⁻) layer 8402 can havethickness ranging from 0.5 to 5 microns and in some cases 0.9 to 2microns and in some cases 1.2 microns and in some cases 1 micron, withresistivity 1 ohm-cm or greater. A surface P⁺ well 8484 can be formed bydiffusion and/or ion implant of P type ions such as B, Al, Ga, In,and/or C, with resistivity of 0.04 ohm-cm or less. In some cases a thinmetal and/or transparent conducting metal oxide such as indium tin oxidecan be deposited in top of the P⁺ well with layer thickness ranging from1 nm to 500 nm prior to microstructure hole etch. The thickness of theP⁺ well can range from 0 nm (Schottky contact) to 500 nm and in somecases from 50 nm to 300 nm. In some cases one or more of the layers canbe GeSi alloy where the Ge fraction can range from 0 to 1.

Microstructure holes 8412 can be inverted pyramids etched with KOHand/or TMAH anisotropic etch with square microstructure holes withlateral dimensions ranging from 300 nm to 1200 nm and in some cases from600 nm to 2500 nm with an etch sidewall angle of approximately 54.7degrees. A period of 900 to 2700 nm. In some cases the side dimensionsof the microstructure holes can range from 900 nm to 1200 nm and aperiod ranging from 1000 nm to 1500 nm with square and/or hexagonallattices. The microstructure holes 8412 can have other cross sectionalshapes such as funnel, cone, cylindrical, trapezoidal, fractal,polygonal, hourglass, keyhole, and any other shapes that can begenerated with wet, dry, electrochemical etching. The microstructureholes can be circular, oval, rectangular, square, polygonal,star-shaped, string shaped, or amoeba shaped. In amicrostructure-photodetector, dimension of the ms-holes (microstructureholes) can be approximately constant. For example, no changes in thelateral dimensions, depth and spacing, and/or any of the dimensions,lateral dimension, depth and/or spacing, can vary in a systematic mannerand/or in a non-systematic manner. For example a random manner and anycombination of systematic and non systematic. This can apply to allMSPD, MSAPD, and other ms-photodetectors.

The MSAPD can have a low reverse bias avalanche voltage of less than−30V and reach QE as much as 1300%, in some cases 1000%, in some cases800%, in some cases 600%, and in some cases 400% at the avalanchevoltage. See, e.g., Kang et al 2008. Data rate bandwidth can range from3 Gb/s to 10 Gb/s, in some cases 10 Gb/s to 40 Gb/s, in some cases 25Gb/s to 50 Gb/s and in some cases 25 Gb/s to 100 Gb/s or higher whenmonolithically integrated with CMOS/BiCMOS ASICs.

In some cases, if the MSPD/MSAPD is released from the substrate inregions directly below the ms-holes, the application of an electrostaticvoltage between the bottom doped layer (anode or cathode) with respectto the substrate can change the spacing of the air gap between theMSPD/MSAPD and the substrate which can result in a tuning effect of theQE with respect to incident wavelength and may be used to furtheroptimize the QE.

In some cases for LIDAR applications, in any of the MSPDs/MSAPDsdescribed in this disclosure, the I or low doped layer for photonabsorption and trapping can have a thickness ranging from 2 to 10microns or more. In such cases the microstructure holes can be partiallyetched into the I layer which in some cases can be GeSi with Ge fractionranging from 0 to 1 and data rate bandwidth can be less than a few Gb/s.Sensitivity (QE or responsivity, gain) and avalanche voltage can beoptimized with the addition of microstructure holes that can reduce theoverall thickness of the APD structure while still maintaining desiredsensitivity as compared to a comparable APD without microstructureholes.

FIG. 85 is a top view of a MSPD/MSAPD integrated with CMOS/BiCMOS,according to some embodiments. In this example the MSPD/MSAPD can be asshown in FIGS. 84A and/or 84B. The inner ohmic contact ring andmetallization 8422 and outer ring ohmic contact metallization 8420 areshown connected to transmission lines that are connected to CMOS/BiCMOSASICs (not shown). A depletion isolation trench 8462 between the anodeand cathode rings is also shown in dotted outline. Several examples ofetch trench/vias 8460 are shown as outside the ms-photodetector. In somecases the etch trench/via can be inside the ms-photodetector as alsoshown in FIG. 85. In some cases, the microstructure holes 8412 can beetched to the BOX layer, in which case, the microstructure holes can beused as a conduit for HP based wet etchant to etch mostly away thesilicon dioxide material underneath the microstructure holes in whichcase etch trench/via may not be necessary in this case. The etchtrench/vias 8460 can be any shape and dimension from circular to polygonto slice of pie shape and dimensions can range from sub microns to multimicrons and perhaps even 10 microns or more. Square microstructure holes8412 are shown etched into the surface doped region 8484 that can be N⁺or P⁺.

Many structures are not shown for simplicity, such as cross overdielectric isolation, thin metal and/or transparent conducting metaloxide layer, hermetic sealing, and planarization effects. The MSPD/MSAPDcan be an array or 2D array that can be monolithically integrated on asingle chip with CMOS/BiCMOS ASICs.

FIG. 86 is a plot showing the results of a FDTD simulation of theoptical field on inverted pyramid holes on 1 micron thick silicon withair interfaces on both the top and bottom. The microstructure holes havethe following dimensions for the simulations: square holes 900 nm on theside; in a square lattice with period 1000 nm (dash curve 8610); and1200 nm (solid curve 8612) over a wavelength span from 800 nm to 1000nm. The vertical axis is enhanced absorption in the 1 micron siliconwith microstructure holes. Anisotropic wet etch with 54.7 degree (111)plane side walls on (100) silicon surface using KOH and/or TMAH basedetchants.

Absorption as high as 90% at 920 nm can be seen in the dash plot 8610and at 850 nm wavelength the absorption is close to 80%. In a similarstructure without ms-holes, the absorption is approximately 5%. Theenhancement is 1600%. Absorption without any recombination is directlyproportional to QE, and in some cases absorption is equal to QE.Air-semiconductor interfaces for both top and bottom can greatly enhancethe QE, and as in high contrast grating the lower the absorption thehigher the Q which compensate for the low absorption and the high Qenhance the QE as the wavelength approach the silicon bandgap wavelengthof 1100 nm at room temperature. Depending on the period, the QE canrange from 20% to over 90% at certain wavelengths in the range 800 nm to1000 nm. In FIG. 2 of Kang et al 2008, at avalanche voltage, the Ge onSi APD can achieve a QE of 1400% and at lower voltage bias withoutavalanche gain the QE is approximately 30% which is approximately 46times gain or approximately a 17 dB gain. With similar layer structure,and with an avalanche gain of 46, the QE of the MSAPD can range fromapproximately 900% to 4000% at certain wavelengths in the wavelengthrange 800 nm to 1000 nm for a silicon MSAPD.

This high sensitivity can be useful to LIDAR applications in addition toits low avalanche voltage and wide wavelength span and can be integratedwith CMOS/BiCMOS ASICs in 1D or 2D arrays. The LIDAR chip can comprisethe MSAPD CMOS/BiCMOS array and an array of VCSELs for generating shortpulses. Other applications include LIFI and other free space opticalcommunications.

The MSPD/MSAPD can be used for both single and multimode fiber for shortreach, reach gap (1250-1350 nm), long reach data center applications andhigh performance computing applications. FTTH (fiber to the home) canalso use MSPD/MSAPD integrated with CMOS/BiCMOS ASICs. With Si and GeSiand Ge on Si, all the wavelengths can be covered using MSPD and/or MSAPDwith enhanced absorption, thinner layers, lower bias voltages, andhigher data rate bandwidths.

A fully integrated MSPD with TIA and other ASICs may resemble structuresdiscussed in Analog Devices Inc. product data sheet, for example, wherea SiGe photodiode was integrated with CMOS TIA and other ASICs for 11.3Gb/s at wavelengths ranging from 1300-1330 nm. With the addition ofmicrostructured holes, the SiGe photodiode I or low doped layer can bemade thinner for higher data rate and also the wavelength range can beextended by 100 nm or more and in some cases by 200 nm or more. And insome cases to 1550 nm wavelength or longer. Responsivity can be 0.3 A/Wor higher at at least one wavelengths in the wavelength span from 1250nm to 1550 nm, and in some cases 0.2 NW or higher at at least onewavelength in the wavelength span from 1250 to 1550 nm. In some casesthe SiGe or GeSi MSPD can have a bandwidth of 25 Gb/s and a responsivityof 0.2 A/W or higher at 1550 nm and in some cases the responsivity canbe 0.3 A/W or higher and in some cases 0.5 A/w or higher and in somecases 0.6 A/W or higher.

At 1350 nm wavelength, the GeSi MSPD can have a data rate bandwidth of25 Gb/s or higher and a responsivity of 0.5 NW or higher and in somecases o.3 A/W or higher and in some cases 0.6 NW or higher and in somecases 0.7 A/W or higher.

In some cases, isolation trenches can be filled with dielectrics such assilicon dioxide and/or silicon oxide. The etch via trenches can befilled in some cases with silicon dioxide/oxide for passivation andhermetic and other purposes to improve performances and reliability. Insome cases the entire MSPD/MSAPD can be covered with a dielectric layersuch as silicon dioxide, or silicon nitride. In some cases silicondioxide may not be stoichiometric and the oxide may be silicon oxide andmay be a mixture of silicon dioxide and silicon oxide.

FIG. 87 is a cross section view of a N-I-P photodiode structure on SOIwith a BOX layer, according to some embodiments. Note that the N and Pcan be interchanged. Not shown for simplicity are structures such as:anode, cathode contacts, mesas, connecting wells, and isolationtrenches. For clarity and simplicity only the microstructure holes andthe N-I-P layers (8710, 8702 and 8704, respectively) on BOX 8708 areshown. The microstructure holes 8712 can have a range of size and shapesand depth and spacing as discussed earlier, however for purposes of thesimulation shown FIG. 88, infra, the microstructure holes 8712 arecircular, 900 nm in diameter with a cylindrical cross section and aperiod of 1200 nm. The holes 8712 are etched to the BOX layer 8708 andare filled with SiO₂ and/or SiO_(x) and have about 10 microns of silicondioxide/oxide 8770 on the top surface. In some cases, the microstructureholes 8712 can be partially filled with silicon dioxide/oxide and insome cases the microstructure holes can be partially etched into the Ior low doped layer 8702. The BOX layer 8708 is 2 microns, the P⁺ layer8704 is 0.3 microns, the I or low doped layer 8702 is 1 micron and theN⁺ layer 8710 is 0.2 microns. 10 microns of silicon dioxide 8770 is ontop of the surface covering the microstructure holes for the FDTDsimulation shown in FIG. 88, infra, of the optical field incident fromthe top surface. Other range of thickness can be used, the P⁺ can rangefrom 0.1 to 0.5 microns, the I or low doped layer can range from 0.5 to5 microns and the N⁺ layer can range from 0.1 to 0.5 microns. Thedielectric in the hole and on the surface can be silicon oxide and/ordioxide, silicon nitride, and/or other insulating dielectrics that canbe polymer for example and the thickness can range from 0 to 20 microns.The microstructure holes can be fully and/or partially filled withdielectrics.

In some cases, the microstructure holes can be formed partially inand/or through the I or low doped layer and in some cases themicrostructure holes can be in the top P or N layer. The holes can betrapezoidal and/or any other shapes such as inverted pyramids andpartially and/or fully filled with silicon oxide and/or dioxide.

In some cases, one or more of the layers can be GeSi where the Gefraction can vary from 0 to 1 where 0 is pure silicon and 1 is puregermanium.

FIG. 88 is a plot showing a FDTD simulation of absorption of theincident photons in the I or low doped layer as a function of wavelengthfrom 800-900 nm for the structure shown in FIG. 87. Absorption can bedirectly proportional to quantum efficiency if all the photogeneratedcarriers are converted to external current. With an external reversebias establishing a high electric field in the I or low doped region,most of the photogenerated carriers can be swept to the anode or cathodebefore the photogenerated carriers can recombine, therefore under theseconditions absorption can be equated to quantum efficiency. Three plotsare shown in FIG. 88 with periods of 1000 nm (curve 8810), 1200 nm(curve 8812) and 1300 nm (curve 8814). Absorption in the I or low dopedlayer or QE can be 50% at certain wavelength ranges for certain periods.For example, for 850 nm and with a period of 1000 nm with 900 nmdiameter microstructure holes the QE can be 50% and at 880 nm wavelengththe QE can be 50% with period of 1300 nm and with microstructure holediameter of 900 nm. In an array of monolithically integrated MSPD/MSAPDwith CMOS/BiCMOS ASICs, each photodiode can be optimized for certainwavelengths by having different periods and/or hole diameter and/or holeetch depth.

According to some embodiments of the present disclosure, the use ofmicro/nano structure holes enables the enhancement of absorption wherethe absorption of the material is weak, especially at wavelengths nearthe bandgap for indirect bandgap semiconductors such as silicon andgermanium. By enhancing absorption, thinner layers can be used toachieve higher data rate bandwidth with good quantum efficiency and alsolower bias voltages for microstructure avalanche photodiodes.

Usable wavelengths for Si MSPD can be extended to 1000 nm. See, e.g.;Gao et al, High Speed Surface Illuminated Si Photodiode UsingMicrostructured Holes for Absorption Enhancements at 900-1000 nmWavelength, DOI: 10.1021/acsphotonics.7b00486 (incorporated herein byreference). This is a is a wider range than GaAs based photodiodes.

In some cases, a BOX layer is desirable when the wavelength is abovebandgap wavelength of silicon since a BOX layer and/or other methods, asdiscussed earlier, disrupts the photogenerated carriers in the substratefrom diffusing slowly back to the high field region in the I or lowdoped layer under reverse bias. The phenomenon of the carriers diffusingback could result in a slow tail in the response of the MSPD/MSAPD thatcan degrade the data rate bandwidth of the MSPD/MSAPD. For opticalsignal wavelengths that are below the bandgap wavelength of silicon, thesilicon can be mostly transparent and will not generate significantphotocarriers in the substrate and the BOX and/or methods to disrupt thelifetime and/or diffusion of photogenerated carriers back to the highfield region is less important and may not be provided. GeSi and/or Geon Si I or low doped layers that absorb in the wavelength region nearand/or below the bandgap wavelength of silicon will generateinsignificant amount of photocarriers in the silicon substrate andtherefore not cause a degradation of the data rate bandwidth of theMSPD/MSAPD.

However in both cases, above or below the bandgap wavelength of silicon,a BOX and/or where the BOX is etched mostly away under themicrostructured holes, will provide a reflection at thesemiconductor-dielectric and/or semiconductor-air interface to result ina higher quantum efficiency which is desirable for MSPD/MSAPD devices.

In some cases, a buried O or N ion implant such as for layer 8314 ofFIG. 83 can be implemented in a FEOL process prior to MSPD/MSAPD layerstructure growth to improve the QE. In some cases the buried oxideand/or nitride layer can be etched entirely and/or partially away inregions under the microstructure holes by either using themicrostructure holes itself as a etching conduits and/or a separateetching trench as discussed earlier to remove fully and/or partially theburied oxide and/or nitride regions under the microstructure holes.Other buried layers can be formed using ion species other than O and/orN such that the buried region can be selectively etched away fullyand/or partially to allow a semiconductor-air interface.

FIG. 89 is a cross section view of an MSPD, according to someembodiments. The structure is similar to that shown in FIG. 84A exceptit is not formed on a SOI wafer. A FEOL process on a bulk silicon wafer8900, P type in this example (but can be N type with P and Ninterchanged) implants buried O and/or N ions to create a buried mostlyoxide and/or mostly nitride region 8934. This region 8934 can be used toprovide a refractive index difference between the silicon and region8934 that reflects light back to the microstructure holes for furtherabsorption enhancement. In addition, for above bandgap optical signalradiation, this region can also inhibit the diffusion of photogeneratedcarriers in the substrate from diffusing back to the high field regionin the I or low doped region that has a reverse bias applied.

In some cases the mostly oxide and/or nitride region 8934 can beselectively etched by dry and/or wet and/or vapor mostly and/or entirelyaway so that the region below the microstructure holes can be mostlyand/or entirely air such that the optical field impinging from the fromsurface travelling through the semiconductor sees a semiconductor-airinterface at the bottom beneath the microstructure holes 8912. This canprovide a higher refractive index contrast and can result in a higherpercentage of reflecting optical signal and/or light. The buried oxideand/or nitride 8934 can be etched through the microstructure holes 8912if the microstructure holes are etched all the way to the buried oxideand/or nitride region. In some cases the holes 8912 can be etched pastthe buried region 8934. As shown in FIG. 89, cylindrical microstructureholes 8912 are etched to the buried oxide and/or nitride region 8934. Insome cases, as in FIG. 84A where the microstructure holes are not etchedto the buried oxide and/or nitride region, etch trenches 8960 can beused to etch the buried oxide and/or nitride region as shown.

In some cases, instead of a highly doped connecting well, a deep trenchwith oxide 8970 on its sidewalls and the center can have conductingsilicide 8972 and/or metal as shown in FIG. 89 which is similar to Kanget al 2008.

The FEOL buried oxide and/or nitride can be formed by a selective areaion implantation. In some cases other species of ions can also be usedto generate a buried region that can be selectively etched to create aburied cavity.

In FIGS. 84A/B and 89, the microstructure holes as in other MSPD/MSAPDstructures can have cross sectional shapes such as cylindrical, funnel,cone, inverted pyramids, trapezoidal, hourglass, ball-like, or acombination of shapes. The holes can have a diameter ranging from 300 nmto 3000 nm with spacing ranging from 50 nm to 5000 nm. The spacing canbe periodic, aperiodic, random or a combination of periodic, aperiodicand random. The depth of the microstructure holes can range from 50 nmto 10000 nm. In some cases the microstructure holes can be on asuperstrate and do not penetrate the photodetector structure. Thesuperstrate can be a high K dielectric such as hafnium oxide and in somecases not a high K dielectric. In some cases the superstrate can beanother semiconductor, in some cases the superstrate can be transparentconducting metal oxide, in some cases can be a dielectric and in somecases it can be metal and/or conducting material. In some cases thesuperstrate can be a combination of dielectric, semiconductor, aconducting material such as metal and/or metal like, polymer and/orconducting polymer. In some cases a superstrate with microstructureholes on top of photodiode and avalanche photodiode can be used withoutthe microstructure holes penetrating the photodetector structure. And insome cases the microstructure holes can penetrate both the superstrateand the photodetector structure and in some cases the holes in thesuperstrate and the photodetectors are not the same.

In some cases microstructure holes can be used to enhance the absorptionof direct bandgap materials such as materials in the III-V family incases where the absorbing layer is thin to the point where theabsorption efficiency is poor. For example, GaAs at 850 nm wavelengthand with the absorbing I or low doped layer of 1 micron or less, the QEcan be 40% or less. The addition of microstructure holes can increasethe QE by a factor of 2 or more. The same principle can be applied toother material in the III-V family such as InGaAs, InP, InGaAsP, AlGaAs,GaN, InN, AlGaN, InGaN, and AlN. The thin I or low doped layer isimportant for high bandwidth operation of the photodiode and/oravalanche photodiode. In addition, other material such as a-Si,polymers, CdS, can also benefit from the absorption enhancement of themicrostructure holes for imaging, night vision scopes, and LIDAR.Wavelengths can range from 800 nm to 2000 nm depending on the materialsystem. Enhancement of absorption and/or quantum efficiency can be afactor of 1.1 or greater and in some cases factor of 2 or greater forstructures with microstructure holes over devices without microstructureholes, for absorbing layer(s) that have QE of 50% or less, in some cases40% or less and in some cases 20% or less. The low QE can be due to theabsorbing layer being 1 micron or less in thickness, in some cases 2microns or less in thickness, and in some cases 5 microns or less inthickness.

According to some embodiments of this disclosure, using microstructureholes for enhancing absorption in a reverse biased photodiode can beapplied to both indirect bandgap material and/or direct bandgap materialand also other materials such as a-Si, a-Ge, A-GeSi, graphene,photosensitive polymers, and semiconducting oxides.

In some cases, in a forward biased diode application, the microstructureholes can enhance the interaction of photons with the gain in amaterial. For example, microstructure holes in a vertical cavity surfaceemitting laser can enhance the photon-gain interaction that can resultin a more efficient laser and/or higher modulation bandwidth laser. Insome cases, the microstructure holes can enhance the light output of alight emitting diode and/or the modulation rate of a light emittingdiode.

As in the case of MSPD, microstructure holes can be etched through the Por N region and into or through the I or low doped region of a verticalcavity surface emitting laser and/or a light emitting diode.Applications include LIDAR laser arrays, detector arrays, lighting,LIFI, data centers, high performance computer, fiber to the home, andenterprise.

FIG. 90 is a cross section view of a MSPD PIN structure that can bemonolithically integrated with CMOS/BiCMOS ASICs on a SOI wafer,according to some embodiments. Note that the CMOS/BiCMOS ASICs are notshown. In this example, the PIN layer thicknesses are approximately 0.2,1.5 and 0.2 microns respectively and with resistivity of 0.1 ohm-cm orless for the P and N regions and 1 ohm-cm or greater for the I or lowdoped region 9002. The thicknesses of the P region 9010 and N region9004 can vary from 0.05 to 0.5 microns and the thickness of the I or lowdoped region 9002 can vary from 0.4 to 5 microns. In this example forFDTD simulation of the optical field as it impinges from the top surface(shown in FIG. 91, infra), the microstructure holes 9012 are square witha side dimension of 900 nm and with a period of 1200 and 1300 nm in asquare lattice. The cross section of the holes are trapezoidal, with aside wall angle of approximately 70 degrees and are filled with silicondioxide to a thickness of 10 microns above the surface. Themicrostructure holes are etched to 0.3 and o.5 microns. The BOX layer9008 is 1 micron. In some cases, the microstructure holes 9012 can haveother cross sectional shapes such as cylindrical, funnel, cone, invertedpyramids, fractal, hourglass, square, polygonal, trapezoidal with sidewall angle ranging from about 160 to 20 degrees, or a combination ofshapes. The plan view shapes of the holes can shapes such as circular,oval, rectangular, square, triangular, hexagonal, polygonal,hourglass-shaped, amoeba shaped, star shaped, or fractal shaped. Thelateral dimensions at the surface can range from 300 nm to 3000 nm ormore. Spacing can range from 50 nm to 5000 nm or more. The spacing canbe random, periodic, aperiodic or a combination. The microstructure holedepths can range from 50 nm to 10000 nm or more and in some casesmicrostructure holes are not etched in the PIN, NIP, PIPIN, PIPN, NINIP,NINP layer structures but rather on a superstrate above thephotodetectors. The silicon dioxide can be other dielectrics such assilicon oxide, silicon nitride, hafnium oxide, polymer, and/or anycombination of dielectrics and can be fully and/or partially filling themicrostructure holes and can be on the surface with thicknesses rangingfrom 0 to 10 microns or more, as depicted in FIG. 90 as layer 9070.

In some cases the microstructure holes 9012 are passivated and notfilled with dielectric and in some cases the microstructure holes arepassivated and filled fully and/or partially with dielectrics.

For simplicity, anode, cathode, connecting wells, connecting electrodes,passivation, anti reflection coatings, transmission lines to CMOS/BiCMOSASICs and other components are not shown.

FIG. 91 is a plot showing a FDTD simulation of the optical field from800-900 nm wavelength impinging on the top surface of a structure shownin FIG. 90. The vertical axis shows the absorption of the photons in theI or low doped region 9002 (shown in FIG. 90) that is directlyproportional to QE and in some cases without recombination and/orscattering, equivalent to QE. The horizontal axis is the incomingoptical signal or light wavelength from 800-900 nm. The microstructureholes are square with 900 nm sides in a square lattice with period of1200 nm and 1300 nm and the ms-holes are etched to 0.3 and 0.5 micronsdeep and filled with SiO₂ and have SiO₂ above the surface to a thicknessof 10 microns. Curves 9110, 9112 and 9114 represent the hole depth andperiods according to inset legend. The absorption in the I or low dopedlayer and/or the QE of the MSPD can be 50% or greater at 850 nm for both0.3 and 0.5 etch depth and with period of 1200 nm. At 880-900 nmwavelengths the QE can be 60% or higher. The QE range from approximately30 to 60% over the wavelength span and where at some wavelegnths the QEcan be as high as 60% or higher. This can be a factor of 2-10 or morehigher than a comparable PIN photodiode without microstructure holes.

FIG. 92 is a cross section view of a two-dimensional (2D) materialphotodetector that can have an absorption enhancement by employing microand/or nano holes for photon trapping, according to some embodiments. Inthis example, the 2D material 9270 can be as discussed in Fiori et al,Electronics based on two-dimensional materials, PUBLISHED ONLINE: 6 Oct.2014 I DOI: 10.1038/NNANO.2014.207 (incorporated herein by reference);Ref. Molle et al, Buckled two-dimensional Xene sheets, PUBLISHED ONLINE:16 Jan. 2017 DOI: 10.1038/NMAT4802 (incorporated herein by reference);and Ref. Mak et al, Photonics and optoelectronics of 2D semiconductortransition metal dichalcogenides, PUBLISHED ONLINE: 31 Mar. 2016| DOI:10.1038/NPHOTON.2015.282 (incorporated herein by reference). The 2Dmaterial 9270 can be sandwiched between two structures 9272 and 9274with micro and/or nano holes 9212 for photon trapping and where thematerial in 9272 and 9274 can be high K dielectrics such as hafniumoxide and in some cases can be non high K dielectrics. The photontrapping structure can enhance the quantum efficiency of the 2D materialfor detecting photons in the wavelength range of visible to infrared tofar infrared. Contacts 9220 and 9222 are make to the 2D material and avoltage and/or current bias can be applied to the contacts forcollecting the photogenerated carriers in the 2D material and in somecases no bias need to be applied when operating in a photovoltaic mode.In some cases the 2D material can be stacked with spacer layers ofdielectric and contacts can be made to each layer to further improve theQE of the 2D material photodetector efficiency. The micro/nano structureholes 9212 can extend through the 2D material 9270 and/or in some casesnot extend through the 2D material and only in the top and/or bottomdielectric and/or silicon 9202. The nano/micro structure holes 9212 canhave lateral surface dimensions ranging from 30 nm to 5000 nm or moreand spacing between the nano micro structure holes can range from 10 nmto 10000 nm or more. The holes can be shaped as a circle, oval, square,polygon, hourglass, fractal, amoeba, star or a combination of shapes.The cross section of the micro nanoholes can be cylindrical, funnel,cone, inverted pyramids, trapezoidal, fractal, and any other crosssections or combinations that can be achieved by dry, wet,electrochemical, focused ion beam, vapor or any other etching andcombination of etching methods. Other layers not shown can include thinmetal, amorphous semiconductor, III-V semiconductor, conducting and/orinsulating polymers, glass, doped glass. In some cases, the 2Dphotodetector arrays and/or stacked arrays can be monolithicallyintegrated with CMOS and/or BiCMOS electronics. In some cases the 2Dmaterial can be functionalize to detect chemical species where the QEcan change with such detection such that the output voltage and/orcurrent from the contacts can change under a constant illumination oflight at certain wavelengths. A superstrate 9274 can be used where themicro/nano microstructure holes can be etched without penetrating the 2Dmaterial and where the superstrate can be a dielectric and/orsemiconductor and/or conductor and any combination thereof. In somecases only the substrate 9200 have micro nano holes and the substratecan be conducting, dielectric, semiconducting and/or any combinationthereof.

FIG. 93 is a cross section view of a MSPD PIN structure similar to thatshown in FIG. 90, according to some embodiments. The structure is alsosimilar to those described elsewhere herein of microstructure holes onsuperstrates in contact with an MSPD/MSAPD. FIG. 93 shows a simplepartial cross section schematic of a PIN photodiode structure on SOIwafer that can be monolithically integrated with CMOS and/or BiCMOSelectronics. The electronics can include a TIA(s) and/or other ASICs forapplications in datacenters, LIDAR, HPC, other optical purposes and/orimaging purposes. The PIN thicknesses are shown for simulation purposesand can range from, N layer 0.05 to 0.5 microns, I layer 0.5 to 5microns and P 0.05 to 0.5 microns. The N and P layer can haveresistivities of 0.1 ohm-cm or less and the I or low doped layer canhave resistivity of 1 ohm-cm or more. The top P layer (or N layer if Pand N are interchanged) can have a thin metal layer and/or transparentconducting metal oxide layer with thicknesses ranging from 1 nm to 100nm or more. A dielectric layer 9370 can be deposited on the top surfaceand can be a high K dielectric layer(s) and/or silicon oxide and/orsilicon nitride layer(s) and/or polymer layer(s) and/or spin on glasslayer(s), with thicknesses ranging from 0.1 to 10 microns or more.Microstructure holes (and/or nanostructure holes) 9312 can be etchedinto the dielectric partially (9314) and/or entirely (9316) and/orthrough the dielectric and into the semiconductor (9318). Etch depth ofthe microstructure holes can range from 50 nm to 6000 nm or more.Microstructure hole lateral dimensions can range from 200 nm to 5000 nmand spacing between microstructure holes can range from 50 nm to 5000nm. The spacing can be periodic, aperiodic, random or a combinationthereof. Microstructure holes 9312 can be circular, oval, cross,polygonal, square, or amoeba shaped. The cross section can be shaped asa cylinder, funnel, cone, fishbowl, trapezoidal, box, inverted pyramid,or combination thereof. In some cases, the structure can be an avalanchediode of PIPIN or NINIP or PIPN or NINP. In some cases one or more ofthe layers can be GeSi with Ge fraction ranging from 0 to 1.

In some cases the BOX layer may not be necessary when the photon energyis below or near the bandgap energy of silicon where photogeneratedcarriers outside the high field region and in the silicon region can beless significant. In some cases the BOX layer can be etched partiallyand/or completely away in regions under the microstructure holesapproximately and can extend beyond the regions under the microstructureholes as discussed earlier for example. As discussed earlier, MSPD,MSAPD with BOX layers can have the BOX layer etched partially and/orentirely away in regions under the microstructure holes by using etchtrenches for example. The BOX and/or semiconductor-air interface canprovide a higher enhancement of the absorption due to reflection at thesemiconductor-dielectric and/or semiconductor-air interface.

The operational wavelength can range from 800-1000 nm, in some casesfrom 850 nm to 1250 nm, in some cases from 1250-1350 nm, in some casesfrom 1350 to 1550 nm, in some cases from 1350 nm to 2000 nm, in somecases from 950 nm to 1200 nm, in some cases 900 nm to 1350 nm and insome cases from 840 nm to 1350 nm. QE can be 30% or higher at at leastsome wavelengths in the span. In some cases QE can be 50% or higher atat least some wavelengths in the span, and in some cases the QE can be70% or higher at some wavelengths in the span. Data rate can range from1 to 100 Gb/s, in some cases 10 to 25 Gb/s, in some cases from 25-50Gb/s and in some cases 60 Gb/s or higher.

Not shown are the anode, cathodes, connecting electrodes/wells,transmission lines to the CMOS/BiCMOS electronics, passivations,antireflections, and other necessary elements to complete a working andoperational photodetector integrated with silicon electronics. A reversebias is applied between the anode and cathode. The MSPD/MSAPD can bemonolithically integrated with silicon electronics for applications inoptical interconnects, LIDAR, image processing for example.

FIG. 94 is cross section showing a structure similar to FIG. 80 exceptwith the addition of a superstrate as shown in FIG. 93. In some cases, aBOX etch trench can also be provided. The superstrate 9470 as in FIG. 93can be a high K dielectric such as hafnium oxide and/or simply siliconoxide and/or silicon nitride and/or polymer with similar thicknessranges and microstructure hole ranges and parameters as in FIG. 93. Inaddition, as in FIG. 93, a thin metal and/or transparent conductingmetal oxide can be added to the top surface of the P layer 8084. BOXetch trenches 9460 can be included for etching the BOX layer 9408partially and/or entirely away in regions under the microstructure holes9312 and vicinity. And in some cases the BOX layer 9408 may not beprovided. In some cases, one or more layers can be GeSi where the Gefraction can range from 0 (all silicon) to 1 (all germanium). Not shownare passivations, transmission lines to CMOS/BiCMOS electronics that canbe monolithically integrated with the MSAPD.

The operational wavelength can range from 800-1000 nm, in some casesfrom 850 nm to 1250 nm, in some cases from 1250-1350 nm, in some casesfrom 1350 to 1550 nm, in some cases from 1350 nm to 2000 nm, in somecases from 950 nm to 1200 nm, in some cases 900 nm to 1350 nm, and insome cases from 840 nm to 1350 nm. QE can be 60% or higher at at leastsome wavelengths in the span, in some cases QE can be 90% or higher atat least some wavelengths in the span, and in some cases the QE can be150% or higher at some wavelengths in the span. Avalanche gain can rangefrom 2-20 dB or more with reverse bias voltage applied to the anode andcathode ranging from −10 to −45 volts and in some cases to −50V.

Data rate can range from 1 to 100 Gb/s, in some cases 10 to 25 Gb/s, insome cases from 25-50 Gb/s, and in some cases 60 Gb/s or higher.

Not shown are the CMOS/BiCMOS ASICs. The MSPD/MSAPD can bemonolithically integrated with CMOS/BiCMOS ASICs in arrays for paralleloptical and/or for CWDM optical communication, for LIDAR, for imagingprocessing applications and/or other sensor applications. For LIDARapplications, see, e.g., Takai et al, Single-Photon Avalanche Diode withEnhanced NIR-Sensitivity for Automotive LIDAR Systems, Sensors 2016, 16,459; doi:10.3390/s16040459 (incorporated herein by reference).

In some cases, the superstrate 9484 can be crystalline and/ornon-crystalline, can be epitaxially deposited on the MSPD/MSAPDstructure and/or deposited by other methods such as e-beam deposition,chemical vapor deposition, plasma enhanced chemical vapor deposition,and sputtering. The superstrate 9484 can be spun on such asspin-on-glass and/or polymer. The superstrate 9484 could also be bondedto the photodetector assembly by soldering, by Van Der Waals force suchas lift-off epitaxy where thin layers are held together by Van Der Waalsforce, and/or by wafer bonding where pressure and heat can be applied tobond the superstrate to the semiconductor comprising the photodetector.Other methods may include gluing the superstrate to the semiconductor.In addition to microstructure holes 9312 and/or pillars on thesuperstrate for absorption enhancement by providing some lateralpropagating and/or standing and/or leaky and/or evanescent and/or nonpropagating and/or radiating optical modes in the semiconductor forexample can enhance the absorption at certain wavelengths. The dimensionof the microstructure holes and/or pillars can range from 100 nm to50000 nm and the spacing between the microstructure holes and/or pillarscan range from 100 nm to 5000 nm depending on the operationalwavelengths which can range from 500 nm to 10000 nm. The depth of themicrostructure holes and/or pillars can range from 30 nm to 10000 nm.The holes can have cross sections that are in the shapes of a funnel,cone, cylindrical, rectangle, polygon, inverted bell, inverted pyramid,hourglass, ball, or a combination thereof. In some cases, thesuperstrate can be a semiconductor and/or an insulator that istransparent and/or mostly transparent to the incident optical signal.

Applications for enhancement of absorption of photons at certainwavelengths and/or wavelength ranges, can include: LIDAR; imaging suchas for camera sensors; high speed optical communication; chemicalsensors; and night vision. For camera sensor applications, absorption ofphotons at at single and/or multiple wavelength ranges can be used wheresensors are provided in an array and/or stacked where shorterwavelengths can be absorbed first and longer wavelengths absorbed last.

The microstructure holes and/or pillars can also be used for enhancedemission of photons such as for light emitting diodes and/or verticalcavity surface emitting lasers in cases where a forward bias can beapplied to the anode and cathode of a PN or PIN semiconductor structure.In some cases, for LIDAR applications, the I or low doped layer forphoton absorption and trapping can have a thickness ranging from 2 to 10microns or more and the microstructure holes can be partially etchedinto the I layer which in some cases can be GeSi with Ge fractionranging from 0 to 1.

FIGS. 95A and 95B are plots showing a FDTD simulation of the opticalfield absorption in the I or low doped layers of FIGS. 93 and 94 forholes 9314 and 9318 in silicon dioxide and hafnium oxide superstrateswith microstructure holes 9312 etched to certain depths as a function ofincident optical wavelength from 800 to 1000 nm. In both FIGS. 95A and95B the holes are square with a side dimension of 900 nm and a period of1200 nm in a square lattice. In FIG. 95A, the holes are etched to adepth of 1.5 microns and shows approximately an average of 30-35%absorption in the I or low doped layer for either the silicon dioxide orthe hafnium oxide. Some of the resonance may be due to interferencesbetween the dielectric layers at the bottom and top of thephotodetector, as in the case of a resonant photodiode. In case FIG.95C, the microstructure holes are etched to a depth of 3.3 microns, orapproximately 0.3 microns into the semiconductor, shows an approximateaverage of 50-55% absorption in the I or low doped layer of FIGS. 93 and94. The resonance is less pronounced as in FIG. 95A, and may havelateral modes in the I or low doped region in addition to other opticalmodes resulting in higher absorption enhancements and therefore higherquantum efficiency and/or responsivity.

FIG. 95C as in FIGS. 95A-95B are square holes in a square lattice withthe same dimensions but etched to different depths in a 3 microns thicksilicon dioxide superstrate that is deposited on the siliconphotodetectors, the etched depths are 0.5 microns above the siliconsurface (curve 9514), at the surface (curve 9516) and 1 microns blow thesurface (curve 9518). The absorption is plotted as a function ofwavelength from 800-900 nm. In some cases the absorption and thereforethe quantum efficiency can be as high as 70% at certain wavelengths buton average the enhanced absorption is between 40-50%. In some cases, oneor more layers can be replaced with GeSi where the Ge fraction can varyfrom 0 to 1.

FIG. 96 is a cross section view of a lateral P-I-N photodiode structurethat is surface illuminated, according to some embodiments. Although thephotodiode is shown in a P-I-N configuration some cases it can be ametal semiconductor metal (MSM) structure and in some cases it can be aN-I-N or P-I-P structure. The I layer 9602 can be intrinsic and/or havea resistivity of 10 to 100 ohm-cm or higher and in some cases 1 ohm-cmor higher. P⁺ well 9606 and N⁺ well 9604 can be implanted and/ordiffused to depths of 0.5 to 5 microns for example, and in some cases 1to 3 microns. Microstructure holes 9612 can be etched in the region of9612 between the P⁺ and N⁺ region as shown, The P⁺ and N⁺ wells 9606 and9604 can have a resistivity of 0.1 to 0.001 ohm-cm or less. The distancebetween the P⁺ and N⁺ wells 9606 and 9604 can range from 2-50 microns ormore. A reverse bias can be applied on the anode and cathode withvoltages ranging from −2 to −30 volts, and in some cases −3V and in somecases −2 to −10V. The photodetector structure can be grown on a SOIsilicon wafer and in some cases on a silicon wafer without a BOX.Microstructure holes 9612 as in described herein supra, can have avariety of shapes and sizes, and cross sections, including circular,oval, square, polygonal, bowtie shaped, star shaped, and keyhole shaped.The cross sectional shapes can be any shape including: funnel, cone,inverted pyramid, cylindrical, ball, fractal, or combinations thereof.The holes 9612 can be formed by dry and/or wet etching. Lateraldimensions can range from 100 nm to 5000 nm, in some cases from 500 nmto 3000 nm, and in some cases from 400 nm to 2500 nm. Spacing betweenadjacent microstructure holes can range from 100 nm to 5000 nm and insome cases from 200 nm to 1000 nm. Depth of the holes can range from 100nm to 10000 nm and in some cases superstrates can be used as discussedearlier. The electric field applied externally via a reverse biasbetween the anode and cathode can be predominately perpendicular and/oralmost perpendicular to the optical incident ray direction. This is incontrast to many earlier configurations where the electric field betweenthe anode 9620 can cathode 9622 can be predominately parallel and/orapproximately parallel to the incident optical ray direction.

From FDTD simulations, the incident optical waves interact with themicrostructure holes and can generate a very complex optical modepattern with complex optical field directions. The directions can beparallel, perpendicular and/or at some other angle to the applied DCfield as a result of the reverse bias voltage applied at the anode andcathode. This set of complex optical modes and fields can enhance theabsorption of the incident photons in the semiconductor. Photonsabsorbed in the I or low doped region can contributed to the high datarate bandwidth response of the photodetector whereas photogeneratedcarriers outside the high electric field region of the I or low dopedlayer due to the reverse bias voltage, can result in a degradation ofthe high speed data rate bandwidth of the photodetector.

In some cases, one of more layers in FIG. 96 can be GeSi with the Gefraction x ranging from 0 to 1 (Ge_(x)Si_(1-x) where x can range from 0to 1). This can be applied to all the photodetector structures describedelsewhere herein.

According to some embodiments the structure shown in FIG. 96 can includemultiple interleaving fingers of P⁺ and N⁺ regions to increase the areaof the photodetector for example. The structure can be integrated withCMOS/BiCMOS ASICs into a single monolithic chip. The ASICs can includeCDR, LA, TIA, and Equalizers. See, e.g., Ref. Kao et al.

FIG. 97 is a top view of the structure shown in FIG. 96, according tosome embodiments. The structure includes an array of microstructureholes 9612 for absorption enhancement and therefore quantum efficiencyenhancement. Also shown are integrated CMOS/BiCMOS ASICs 9770 for signalprocessing and enhancements and for further data analysis and/ortransmission to other electronic circuits. An electrical isolationtrench 9760 can be included to separate any potential electricalinterference between the photodetector and the ASICs. Transmission lines9780 and 9782 can be used to connect the photodetector to the ASICs. Inaddition, arrays of photodetectors can be fabricated and integrated withCMOS/BiCMOS ASICs into a single monolithic chip 9700. Optical signalsilluminate the surface and in some cases superstrates can be used toredirect the optical signal whose rays are parallel to the photodetectorto illuminate at an angle normal and/or almost normal to the surface ofthe photodetector. In some cases one or more layers can be replaced withGeSi where Ge fraction can vary from 0 to 1.

According to some embodiments, the structure shown in FIG. 97 can berepeated, where multiple anodes and multiple cathodes are “interleaved”with an array of microstructure holes between each anode and cathode.Such a structure can be thought of as an interleaved fingers pattern.

FIG. 98 is a top view of an integrated MSPD/MSAPD, according to someembodiments. The MSPD/MSAPDs 9810 can be formed with or withoutsuperstrates, as described herein supra. Monolithically integrated toCMOS/BiCMOS ASICs 9870 can include functionality such as transimpedanceamplifier, clock data recovery, limiting amplifier, and equalizer. Inthe example shown chip 9800 include the ASICs 9870 and MSPD/MSAPDs 9810in a 1×4 configuration (i.e. one ASICs module paired with fourMSPD/MSAPDs. Other configurations such as 1×10, 2×5, and 2×4 are alsopossible. In some examples, the 1×4 configuration shown can be 4×25 Gb/sfor a total of 100 Gb/s or 4×50 Gb/s fora total of 200 Gb/s. TheMSPDs/MSAPDs 9810 can be spaced by 250 microns center to center with thediameter of the photodetectors ranging from 25 to 80 microns and in somecases 30 to 50 microns. An optional electrical isolation trench 9860 canbe included that can be filled with dielectric and/or amorphoussemiconductor. A number of bond pads 9806 can be provided. Not allelements are shown for simplicity. Examples of structure that could beincluded but are now shown include: anti reflection coatings,passivations, planarization effects, transmission lines, mesas, andimplanted wells. Also the correct number of bond pads may not be shown.The chip size can vary from 1.5 mm×1.5 mm to 3 mm×3 mm or more dependingon the number of photodetectors and the ASICs.

In some cases one of more layers can be replaced with GeSi and where theGe fraction can vary from 0 to 1. In some cases, the MSPD/MSAPD with orwithout superstrates can have one or more of its layer made of a III-Vfamily material. The substrate can be made of a III-V family material.The inclusion of microstructure holes in III-V material can enhanceabsorption and therefore the quantum efficiency of thin III-V materialphoton absorbing layer with thicknesses less than 2000 nm for exampleand in some cases with thicknesses equal to or less than 1000 nm. Whenthe III-V or II-VI material is thin for high speed or high data ratebandwidth operation the quantum efficiency and/or responsivity cansuffer from the reduced thickness resulting in reduced absorption ofphotons. With the addition of microstructure holes, the absorption canbe enhanced and therefore the quantum efficiency by a factor rangingfrom 1.5 to 10 or greater as compared to a similar structure withoutmicrostructure holes.

FIG. 99A is a cross section schematic of a microstructure enhanced III-Vphotodiode, according to some embodiments. For further detail of 111-Vphotodiodes, see, e.g., K. W. Carey et al, Characterization ofInP/GalnAs/InP heterostructures grown by organometallic vapor phaseepitaxy for high-speed pin photodiode, Journal of Crystal Growth1986(incorporated herein by reference). The light absorbing region 9902 isan I or low doped InGaAs and/or InGaAsP layer of 1500 nm thickness. TheI layer 9902 cladded by InP P and N type material (layers 9904 and 9906)The substrate 9900 is InP N or be semi insulating. The photodiode isused to detect photons at 1300 nm. To increase the data rate bandwidthof the photodiode, a thinner InGaAs photon absorption layer 9902 can beused to reduce the photogenerated carrier transit time under a reversebias applied between the anode and cathode. The reduced thickness of theInGaAs layer can result in lower quantum efficiency and/or responsivity.Microstructure holes 9912 are etched into the P-I-N structure at depthsranging from 100 nm to 3000 nm. Microstructure holes can be shaped asdiscussed earlier (e.g. funnel, cone, cylindrical, inverted pyramids,etc.), and have lateral dimensions ranging from 300 nm to 5000 nm. Thespacing of the microstructure holes can range from 100 nm to 3000 nm.The microstructure holes can be in a periodic array, aperiodicarrangement or random arrangements. The diameter of the photosensitivearea can range from 10 to 100 microns or more. In some cases thediameter of the photosensitive area can range from 5 to 50 microns. Insome applications where data rate may not be high, but the photonabsorption region needs to be thin, the addition of microstructure holescan enhance the absorption and therefore the quantum efficiency and/orresponsivity. In some cases a superstrate can be utilized as discussedearlier. And in some cases the substrate 9900 can be silicon.

In some cases, a III-V avalanche photodiode can be fabricated withmicrostructure holes in a P-I-P-I-N structure where the I layer betweenthe P layers can be InGaAs and/or InGaAsP and microstructure holes canbe etched partially into the top P layer and/or partially into the Iabsorption layer and/or entirely into the I absorption layer. In somecases, a superstrate as discussed earlier can be implemented on theavalanche photodiode with microstructure holes. See, e.g., Chen et al,Optimization of InGaAs/InAlAs Avalanche Photodiodes, Nanoscale ResearchLetters (2017) 12:33 (incorporated herein by reference) which discussesInP/InGaAs APDs without superstrate or holes. The microstructure holeswith depth from the surface of the semiconductor ranging from 50 nm to3000 nm and can have cross sectional shapes of funnel, cone, invertedpyramids, cylindrical, polygonal and/or any combinations of shapes, andthe microstructure holes (applies to III-V photodiodes also) can becircular, square, polygonal, star, oval, fractal, keyhole and/or anycombination of shapes, with lateral dimensions ranging from 300 nm to5000 nm and with spacing between the microstructure holes ranging from100 nm to 3000 nm or more and can be periodic and/or aperiodic and/orrandom. Wavelength ranges can span from 800-1600 nm depending on theIII-V material combination of binary, ternary and/or quaternary. Quantumefficiency can range from 50% or higher at certain wavelengths and insome cases 70% or higher at certain wavelengths and in some cases 90% orhigher at certain wavelengths and in some cases with avalanche gain dueto a reverse bias between the anode and cathode can be 200% or higherand in some cases 400% or higher at certain wavelengths. Data ratebandwidth can range from 1 Gb/s to 100 Gb/s or higher depending on thethickness of the layers and size of the photodetector that cancontribute to junction capacitance.

In some cases, a superstrate can be used with the III-V APD withmicrostructure holes. And in some cases one or more layers can be II-VImaterial family and in some cases the wafer can be silicon. In somecases one or more layers can be non crystalline and applies to all thestructures discussed.

Applications can include optical data communication, LIDAR, imaging,sensing, and other applications requiring high quantum efficiencyoptical detection that converts photons to electrons for further imageprocessing or information processing. In some cases, the III-Vphotodetector can be a AlGaAs/GaAs structure for wavelengths rangingfrom 800 to 900 nm

FIG. 99B is a plot showing an FDTD simulation of the structure shown inFIG. 99A. The following parameters where used for the simulation:P-AlGaAs (30% Al) 1 micron thick; I GaAs 1 micron thick; N AlGaAs (30%Al) 1 micron thick; and GaAs semi insulating substrate. TheMicrostructure holes were funnel shaped etched 1.5 micron deep, diameter700 nm with a period of 1000 nm in a square lattice. The vertical axisis absorption and the horizontal axis is wavelength in microns. Curve9922 is for the structure without microstructure holes and curve 9920 isfor the structure with microstructure holes. As can be seen, theabsorption and therefore the quantum efficiency QE with microstructureholes on the III-V MSPD can be 2 times or greater than a similar III-Vphotodiode without microstructure holes at at least one or morewavelengths in the span from 800-900 nm for GaAs and 1200 nm to 1600 nmfor InGaAs absorption layers. The reduction in thickness of the I layercan significantly increase the data rate bandwidth of the III-V MSPD to40 Gb/s or higher, in some cases 50 Gb/s or higher, in some cases 80Gb/s or higher and in some cases 100 Gb/s or higher. This is whilemaintaining a QE that is higher than a similar III-V photodiode withoutmicrostructure holes by a factor of 1.5 times or more at certainwavelengths. Optical signals impinge from the top surface and in somecases from the bottom surface and photons are absorbed in the I layer.The same principle can be applied to III-V MSAPDs with the addition ofavalanche layer(s). The addition of microstructure holes in an APD (Si,GeSi or III-V) can increase the QE and sensitivity and responsivity dueto photon trapping over a similar structure without microstructureholes. Other attributes for an APD can be lower avalanche voltages of anAPD with microstructure holes as compared to a comparable APD withoutmicrostructure holes.

FIG. 100 is a cross section of a MSPD, according to some embodiments. APINP photodetector structure is shown with an optional BOX layer. Thestructure could also be a MSAPD with added avalanche layers. Thephotodiode PIN layers 10006, 10002 and 10004 are grown on a P layer10010 such that a second anode 10024 can provide a forward or reversebias between anode 10024 and cathode 10020, while the photodiode PINprovides a reverse bias between the anode 10022 and cathode 10020. Areverse bias between anode 10024 and cathode 10020 can help reduce theeffect of the slow diffusion of photogenerated carriers outside the highfiled I region The forward biasing of the bottom PN layer provides acurrent injection at the interface between the bottom PN junction. Insome cases, with a high enough current injection the P layer 10010 withresistivity ranging from 0.1 to 0.001 ohm-cm or less can change in itsrefractive index and in some cases can become more metallic thereforereflecting more of any photons that were not trapped by themicrostructures back toward the photon trapping microstructure holesand/or other microstructures. This extra reflection of photons at thebottom PN junction can further increase the QE of the MSPD/MSAPD. Insome cases the bias between anode 10024 and cathode 10020 can bemodulating. In some cases the bias can be forward, reverse eithermodulating, DC or both. Mixing, heterodyne, homodyne, of RF withdetected optical signals may improve signal to noise ratio, RFtransmission applications, and other applications requiring highfidelity of signal.

The material can be silicon and/or in some cases one or more layers canbe GeSi with Ge fraction x ranging from 0 to 1. In some cases, thematerial can be a non-silicon material, such as one or more layers beinga III-V family and/or II-VI family material.

Microstructure holes 10012 and/or other microstructures are formed asdescribed herein supra. The lateral dimensions, spacing, cross sectionalshapes, depth, and other parameters such as wavelength, data rates,monolithic integration, QE, responsivity are as in any of the MSPD/MSAPDstructures described herein supra.

In some cases, the PINP MSPD can have gain such as a PNP bipolartransistor. Such MSPDs with gain can be advantageous due to the lowvoltage nature and having transistor like gain.

In some cases the P Si layer 10006 can be 0.2-0.3 microns thick withdoping with boron to concentration greater than 1 10²⁰ ions/cm³. The Ilayer 10002 can have thickness ranging from 1.0 to 2.0 microns withbackground doping concentration of less than 1.5 10¹⁵ ions/cm³. The Nlayer 10004 can have thickness ranging from 0.2-0.3 microns with dopingconcentration of arsenic greater than 1 10¹⁹ ions/cm³, The P devicelayer 10010 can have thickness ranging from 0.1 to 0.25 microns. Theoptional BOX (buried oxide) 10008 can have thickness ranging from 1 to 4microns on silicon handle wafer 10000.

FIG. 101 is a cross section of a MSPD (or MSAPD) with a mesa and theregions under the microstructure holes selectively removed, according tosome embodiments. In this example, the BOX layer 10108 is fully and/orpartially removed to provide a higher refractive index contrast betweenthe microstructure hole semiconductor regions. Instead of silicondioxide, region 10110 can be mostly air which has a refractive index of1 instead of approximately 1.45 for silicon dioxide. This higherrefractive index contrast can further improve the enhancement ofabsorption in the microstructures 10112 and therefore improve the QE andresponsivity. FIG. 101 shows cylindrical holes 10160 that are etched tothe BOX layer 10108 with dimensions similar to the microstructures10112. Microstructures 10112 are not etched all the way to the BOX layer10108 and can be any shape such as inverted pyramids, funnels, cones, orcombination of shapes that can be achieved with dry and/or wet etching.

The microstructured holes 10160 that are etched to the BOX layer canhave lateral dimensions ranging from 300 nm to 3000 nm and can be anarray spaced ranging from 1000 nm to 10000 nm. The shallowermicrostructure holes 10112 can have lateral dimensions ranging from 300nm to 3000 nm and spacing ranging from 50 nm to 3000 nm. Microstructureholes 10112, as discussed earlier, can have surface shapes such ascircular, oval, square, polygonal, hourglass, star, amoeba, fractal, orcombinations of shapes, and cross sectional shapes such as invertedpyramids, funnels, cones, cylindrical, polygonal, hourglasses, balls,fractals or combinations thereof.

In some cases all or mostly all of the microstructure holes can beetched to the BOX layer. In some cases some of the microstructure holescan be etched to the BOX layer and in some cases the microstructureholes that are etched to the BOX layer can be in a periodic array and/oraperiodic ally arranged and/or arranged in a pattern such as circularfor example to further assist confining the photons to regions forphoton trapping with microstructures.

The material in FIG. 101 can be silicon or one or more layers can beGeSi with Ge fraction x ranging from 0 to 1. In some cases, one or morelayers can be a III-V and/or a II-VI material. The MSPD/MSAPD can beoperated with a reverse bias applied between the anode and cathode.Optical signals can impinge from the top surface and in some cases fromthe bottom surface.

Depending on the material, wavelength ranges can range from 800-1550 nmor longer, in some cases from 800 nm to 950 nm, in some cases from 800nm to 1100 nm, in some cases from 1250 nm to 1350 nm, in some cases from1250 nm to 1600 nm and in some cases 800 nm to 880 nm.

QE can range from 30% to 70% or higher at at least one wavelength in thewavelength span. The QE of MSPD and/or MSAPD can be higher than acomparable photodiode and/or avalanche photodiode withoutmicrostructure. Data rate bandwidth can range from 1 Gb/s to 100 Gb/s,in some cases 25 Gb/s to 50 Gb/s, and in some cases 50 Gb/s or higher.

In some cases the P Si layer 10106 can be 0.2-0.3 microns thick withdoping with boron to concentration greater than 1 10²⁰ ions/cm³. The Ilayer 10102 can have a thickness ranging from 1.0 to 2.0 microns withbackground doping concentration of less than 1.5 10¹⁵ ions/cm³. The Nlayer 10104 can have a thickness ranging from 0.2-0.3 microns withdoping concentration of arsenic greater than 1 10¹⁹ ions/cm³. An Ndevice layer (not shown) can exist between 10104 and 10108 having athickness ranging from 0.1 to 0.25 microns. BOX (buried oxide) 10108 canhave thickness ranging from 1 to 4 microns on silicon handle wafer10100. In some cases, the BOX 10108 beneath the microstructure holes canbe partially and/or fully etched away, and in some cases the BOX remainun-etched. The structures shown in FIG. 101 and other Si, GeSi andsilicon based MSPDs/MSAPDs can all be monolithically integrated withCMOS and/or BiCMOS silicon electronics such as TIAs, CDRs, LAs, and/orequalizers. In some cases with heteroepitaxy, III-V MSPDs and/or III-VMSAPDs on silicon based material and substrates can also bemonolithically integrated with CMOS/BiCMOS ASICs in silicon.Applications include optical communications, optical datacommunications, LIDAR, imaging, single photon detections, sensing, andbiometrics. In some cases for LIDAR applications, the MSAPDs describedin the present disclosure can be tailored for the LIDAR wavelengths,responsivity or QE, data rate bandwidth and avalanche voltage. Inparticular, the I or low doped region for photon absorption and trappingcan have a thickness ranging from 2 to 10 microns or more and thephotosensitive area can have a lateral dimension ranging from 50 to 5000microns or more. Arrays of the MSAPDs can be monolithically integratedwith CMOS/BiCMOS ASICs suitable for specific LIDAR applications such asautomotive sensors and/or robotic sensors. Wavelengths can be tailoredand optimized with the addition of GeSi with Ge fraction ranging from 0to 1 to address wavelengths from 700 nm to 2000 nm. Low avalanchevoltages can be achieved with the addition of microstructure holes toreach desired QE and responsivity with reduced overall thickness of theAPD structure for higher reliability in hostile environments. Themicrostructure holes and the MSAPD can be fully passivated for low darkcurrent. Avalanche gain can take place in an Si I layer for reducednoise characteristics.

In some cases the wavelength used for LIDAR applications is 903 nm andin some cases the wavelength range is 800-950 nm. For these wavelengthsa GeSi alloy I or low doped absorption layer with photon trappingmicrostructure holes can be used in an MSAPD. The microstructure holescan be used to improve the QE and/or responsivity over a comparable APDwithout microstructure holes. The detection range can be extended from100 meters to 250 meters in some cases. In some cases, the avalanchevoltage can be reduced due to reduced layer thickness in a MSAPD ascompared to a comparable APD without microstructure holes.

FIG. 102 is a plot showing an FDTD simulation of the optical fieldabsorption enhancement verses wavelength for a MSPD structure with PIPN,PP-N, PN-N, or PIPIN structure for a MSAPD device, according to someembodiments. The wavelength range is (800-980 nm). The device hasmicrostructure holes in silicon with an I or low doped layer thicknessof 5 micrometers (curve 10212) cladded by 0.2 and 0.4 microns of P and Nlayers on a BOX layer (SOI wafer) for a MSPD structure and with either aPIPN or PIPIN structure for a MSAPD device. The hole diameter is 700 nmand the hole period is 1000 nm in a square lattice and the holes arecylindrical, etched to a depth of 1000 nm for this simulation. Enhancedabsorption at some wavelengths in the range 800-980 nm, can be 80% orhigher and at some wavelengths the enhanced absorption can be 60% orhigher. A comparable silicon photodetector absorption verses wavelengthwithout microstructure holes with 10 micrometers of I or low doped layerand without a BOX layer, is shown in the dashed curve 10214. For asilicon photodetector to reach 80% absorption at some wavelengths in therange of about 800-980 nm, an I or low doped layer of thickness ofapproximately 30 microns may be necessary. Such thick I layer wouldrequire a reverse bias voltage of 100 to 200 volts for APD operation.Even for photodiode operation, a high reverse bias voltage of 20 voltsor higher may be necessary to achieve good quantum efficiency.Absorption can be directly proportional to quantum efficiency and insome cases can be the quantum efficiency if recombination and scatteringare negligible. With the addition of micro and or nano structure holes,a thinner I or low doped layer or region can be used to achieve aquantum efficiency that is approximately equivalent to a thickermicro/nanostructure hole-free I or low doped layer. Reverse biasvoltages of MSPDs can be less than 20 volts and for MSAPD less than 100volts. In some cases the reverse bias voltages for MSPDs can be lessthan 10V and for MSAPDs less than 50V. In some cases the reverse biasvoltages for MSAPDs can be less than 35V. In some cases, for singlephoton MSAPD devices where the MSAPD can be operated at theGeiger-counter mode or beyond the breakdown voltages, the reverse biasvoltage can be less than 25V, in some cases less than 15V, and in somecases less than 10V. The I or low doped layer or region for a singlephoton MSAPD detector can range from 0.3 to 5 microns for example. Insome cases the I layer or region for MSAPDs and or MSPDs can range from0.5 to 6 microns.

The thinner I layer or region of MSPDs, MSAPDs can be more conducive formonolithic integration with CMOS/BiCMOS electronics and the lowerreverse bias voltages can result in high device reliability.

For LIDAR and or LiFi applications the data rate can range from hundredsof Mb/s to tens of Gb/s. Monolithic integration with CMOS/BiCMOS ASICsof arrays of MSPDs can be suitable for such applications. MSAPDs andMSAPD-single photon detectors can be implemented with significant costreduction and improvement in performance due to low parasitics.

In some cases, wavelengths used for LIDAR can range from 780-980 nm, andin some cases from 800 nm to 2000 nm. MSPDs/MSAPDs can cover thesewavelengths with Si and or GeSi I or low doped regions withmicrostructured holes for photon trapping and enhanced absorption.Microstructure holes can be etched or formed in Si and or GeSiphotodiodes, Si and or GeSi avalanche photodiodes, Si and/or GeSi singlephoton avalanche photodiodes, Si and/or GeSi photomultipliers forexample. See, e.g., Hamamatsu data sheet for Si photodetectors forLIDAR,https://www.hamamatsu.com/resources/pdf/ssd/Photodetector_lidar_kapd0005e.pdf,incorporated herein by reference.

In some cases, a thermal anneal and/or passivation can be performedafter the etching and/or formation of the microstructure holes andstructures and/or any mesas and/or any trenches to remove any damage dueto etching. In some cases, the lateral dimension of the photodetectorfor LIDAR can range from 30 microns to 3000 microns or more. In somecases an array of photodetectors can be made such as an array of Si andor GeSi I layer SPAD (Single photon avalanche photodiode) that can befabricated for high sensitivity imaging. The use of microstructure holescan further improve the sensitivity and extend the wavelength of the Siand or GeSi photodetector as compared to a comparable photodetectorwithout microstructures holes or microstructures for photon trapping toenhance the absorption and therefore the QE. QE of photodetectors withmicrostructure holes for absorption enhancement can be formed in thesuperstrate, in the first doped layer, into the low doped or I layer orregion and/or in the second doped region. QE can thereby be enhancementby a factor of 1.5 or more at certain wavelengths in the range 800 to1000 nm for silicon, 900 nm to 1400 nm for GeSi, and 1000 nm to 2000 nmfor Ge. In some cases the QE enhancement factor can be 2 or more timesat certain wavelengths and in some cases the enhancement factor can be10 times or more at certain wavelengths.

FIG. 103 is a cross section of a MSPD or MSAPD having Ge and/or GeSi(with Ge fraction ranging from greater than 0 to 1 where 1 is all Ge,and in some cases from 0 to 1 where 0 is all silicon) layers grown on Sithat is monolithically integrated with CMOS/BiCMOS ASICs, according tosome embodiments. The ASICs can be configured for various applicationssuch as high speed optical data communications using optical fibers,free space optical communications such as LIFI, light direction andranging (LIDAR), and imaging. The layers/regions can be grown on SOI orbulk silicon substrates. Shown in FIG. 103, a BOX layer 10308 is used toprovide higher refraction index contrast to confine the photon trappedlight. As discussed earlier, the BOX layer 10308 can be partially and/orentirely removed beneath the photodetector to provide a higherrefractive index contrast which can further improve the QE.

The N+ Si layer 10304 adjacent to the BOX layer 10308 can have aresistivity of 0.02 ohm-cm or less with thickness ranging from 100 nm to1000 nm approximately. Si P layer 10303 can have resistivity of 1 ohm-cmor less with thickness ranging from 50 nm to 500 nm. Ge and/or GeSialloy I and or low doped layer/region 10302 can have resistivity of 0.2ohm-cm or greater with thickness ranging from 100 nm to 5000 nm. Geand/or GeSi P⁺ layer 10306 can have resistivity of 0.05 ohm-cm or lesswith thickness ranging from 50 nm to 1000 nm. In some cases a thin metalor transparent conducting metal oxide such as indium tin oxide (ITO) ofthickness ranging from 5 nm to 1000 nm can be added to the top layer toreduce the series resistances.

In some cases, the Ge and/or GeSi layers 10302 and/or 10306 can be grownby selective area growth where dielectric layers such as silicon oxide,nitride for example, 10364 can be used to cover areas on the silicon toprevent crystalline or mostly crystalline Ge or GeSi growth. An array ofdielectric pattern of rectangular, polygonal, circular, oval and/or anyother shapes can be deposited or otherwise formed on the Si 10303 suchthat during selective area growth of Ge/GeSi, those areas withdielectric will be void and or mostly void of high quality Ge/GeSi suchas crystalline or mostly crystalline. These voids can be calledmicrostructure holes. The dielectric thin film pattern can be periodicand/or aperiodic with nearest edge to edge spacing ranging from 50 nm to3000 nm and with lateral dimensions ranging from 100 nm to 3500 nm ormore.

The microstructure holes 10312 formed using selective area growth areshown as holes “C” in FIG. 103. The sidewalls of the holes “C” may notbe vertical as shown but may have slope depending on the thickness ofthe Ge/GeSi and growth conditions and crystal orientations. The Cmicrostructure holes can be further etched to improve MSPD/MSAPDperformances if necessary. In some cases, additional holes can be etchedinto the Ge/GeSi layers after selective area growth as shown in holes“A” and “B” where holes “A” can be an inverted pyramid and “B” can becylindrical and or funnel or cone and/or any combination of shapes usingdry and/or wet etch. The microstructure holes can be etched to depthsinto the first doped layer (P⁺) 10306 and/or into the I or low dopedGe/GeSi layer/region 10302. As discussed elsewhere herein, thermalannealing and/or passivation can be used to reduce leakage current dueto etching damages and/or exposed surfaces. The wavelength range ofoperation can be from 800 nm to 1650 nm or longer depending on thecomposition of GeSi alloy and/or Ge and whether the layers are strainedor relaxed. Data rates can range from less than 1 Gb/s to 50 Gb/s orhigher depending on photodetector layer structure and diameter.

In the case of MSAPDs, a reverse bias voltage ranging from −5 to −35volts can be applied to the anode 10320 and cathode 10322 (shown formedin a mesa/trench etch 10360) and can operate in either the avalanchemode and/or the persistent avalanche mode. In the case of MSPDs, the SiP 10303 layer may not be necessary and a reverse bias voltage of −2 to−10 volts can be applied to the anode 10320 and cathode 10322. In somecases, selective area growth may not be necessary and microstructureholes A and B can be etched into the first doped layer and or into the Ior low doped region. The photodetectors with microstructure holes forphoton trapping can have a QE (or external QE, EQE) greater than acomparable photodetector without microstructure holes for photontrapping for certain wavelengths.

According to some embodiments, the temperature range of operation forthe MSPDs described herein can range from −40 to 95 degrees centigrade,in some cases from −5 to 95 degrees, and in some cases from −40 to 100degrees C.

According to some embodiments, the thickness of the BOX layer forMSPDs/MSAPDs described herein can range from 5 nm to 5000 nm or more andin some cases from 20 nm to 5000 nm or more. In some cases the BOX layeror region can be ion implanted.

According to some embodiments, the pitch between MSPDs/AMSPDs in anarray can range from 100 to 4000 micrometers.

According to some embodiments, high data rate bandwidth of theintegrated chip comprising MSPD/AMSPD and CMOS and or BiCMOS ASICs withclean open eye diagrams can result in bit error rates (BER) of 1E-3 to1E-12 or better for certain data rates in the range of less than 1 Gb/sto 25 Gb/s or higher, in some cases for data rates of 50 Gb/s or higher,and in some cases for data rates of 100 Gb/s or higher. BER also dependson the bit pattern, and any error correcting algorithms and or forwarderror corrections.

Although the foregoing has been described in some detail for purposes ofclarity, it will be apparent that certain changes and modifications maybe made without departing from the principles thereof. It should benoted that there are many alternative ways of implementing both theprocesses and apparatuses described herein. Accordingly, the presentembodiments are to be considered as illustrative and not restrictive,and the body of work described herein is not to be limited to thedetails given herein, which may be modified within the scope andequivalents of the appended claims.

1. A single-chip device comprising an integrated combination of amicrostructure-enhanced photodetector (MSPD) and an active electroniccircuit, both formed on or in a single substrate and configured toreceive an optical input that in cross-section is substantiallycontinuous spatially at least some of time, convert the optical input toan electrical output, and process the electrical output into a processedoutput, wherein: the MSPD on or in said single substrate comprises anintermediate layer, a first layer at one side of the intermediate layer,and a second layer at an opposite side of the intermediate layer,wherein: each of the layers comprises Silicon, Germanium, or an alloythereof; at least one of said layers, or an overlying covering layerthat may be present, has holes intentionally formed therein, extendingin directions transverse to the layers; each of the first and secondlayers comprises a doped material; the intermediate layer comprises amaterial that is less doped than at least one of the first and secondlayers or is undoped, wherein the degree of doping is the same ordifferent for different positions in the intermediate layer; an inputportion configured to concurrently receive at a plurality of said holessaid optical input that has said substantially continuous cross-section;and an output portion configured to provide said electrical output fromthe MSPD; and the active electronic circuit on or in said singlesubstrate is configured to process the electrical output from the MSPDby applying thereto: amplification to form said processed output fromthe single-chip device; processing other than or in addition toamplification to form said processed output from the single-chip device;and routing to one or more selected destinations; and a communicationchannel on or in said single-chip device, configured to deliver theelectrical output from the MSPD to the active electronic circuit.
 2. Thesingle-chip device of claim 1, in which said active electronic circuitis at least partly extends beyond said substrate.
 3. The single-chipdevice of claim 1, in which said active electronic circuit is at leastpartly inside said substrate.
 4. The single-chip device of claim 1, inwhich said overlying layer is present as a superstrate at one side ofsaid first, intermediate, and second layers, and contains said holes. 5.The single-chip device of claim 1, in which said MSPD comprises a III-Vmaterials family photodiode.
 6. The single-chip device of claim 1,further including an air-filled volume between the substrate and theMSPD.
 7. The single-chip device of claim 1, further including a layer ofa dielectric material that covers the holes and is in the propagationpath of said optical input.
 8. The single-chip device of claim 1,further including an avalanche region at one side of the MSPD, formingtherewith an avalanche microstructured photodiode (MSAPD).
 9. Thesingle-chip device of claim 1, in which said holes are present in saidintermediate layer.
 10. The single-chip device of claim 1, in which saidholes are present in said intermediate layer as well as in at least oneof the first and second layers.
 11. The single-chip device of claim 1,in which said holes are present in each of the first, second, andintermediate layer.
 12. The single-chip device of claim 1, in which eachof said first and second layers and said intermediate layer has athickness and at least some of said holes extend through the entirethickness of said intermediate layer and of one of said first layer andsecond layer and through at least a part of the thickness of the otherone of said first and second layers.
 13. The single-chip device of claim1, in which at least some of said holes are shaped as inverted pyramids.14. The single-chip device of claim 1, in which at least some of saidholes have triangular sections in planes transverse to said layers. 15.The single-chip device of claim 1, in which at least some of said holeshave triangular sections in planes transverse to said layers, withvertices within the intermediate layer.
 16. The single-chip device ofclaim 1, in which at least some of said holes have sidewalls that slopein planes transverse to said layers.
 17. The single-chip device of claim1, in which at least some of said holes have sidewalls with pluraldifferent slopes along the inside walls of the holes.
 18. Thesingle-chip device of claim 1, in which at least some of said holesdiffer from each other in at least one of (i) distance by which theholes extend in said directions, (ii) shape of the holes, and (iii)spacing of the holes from each other.
 19. The single-chip device ofclaim 1, in which the holes are in the intermediate layer and whereinone of said first and second layers conformally covers inside walls ofthe holes as well as spaces between the holes.
 20. The single-chipdevice of claim 1, in which the holes are at least partly filled with adielectric material.
 21. The single-chip device of claim 1, in which theholes are entirely filled with a dielectric material.
 22. Thesingle-chip device of claim 1, in which said optical input enters theMSPD through one or both of said first and second layers, and each ofthe first and second layers through which the optical input enters is nomore than 500 nanometers thick.
 23. The single-chip device of claim 1,in which at least one of the first layer, the second layer, and theintermediate layer comprises a material represented by Ge_(x)Si_(1-x),where x is greater than zero.
 24. The single-chip device of claim 1, inwhich said MSPD further comprises ohmic contacts configured forreverse-biasing the MSPD.
 25. The single-chip device of claim 1, inwhich the MSPD further includes ohmic contacts to said first and secondlayers, at least one of said ohmic contact being through a via in saidsubstrate.
 26. The single-chip device of claim 1, further comprising alight guide to said MSPD for directing said optical input thereto, andelectrical contacts from the active electronic circuit configured tocarry said processed output out of the single-chip device.
 27. Thesingle-chip device of claim 1, further comprising a light guide to saidMSPD configured to bend the optical input from an initial propagationdirection to a propagation direction transverse to said layers, andelectrical contacts from the active electronic circuit configured tocarry said processed output out of the single-chip device.
 28. Thesingle-chip device of claim 1, further comprising one or more additionalMSPD on or in the same substrate, and respective different opticalbandpass filters coupled with at least two of the MSPDs on or in saidsingle substrate, whereby at least two of said MSPDs are configured torespond to different wavelength ranges that are within said opticalinput.
 29. The single-chip device of claim 1, further comprising one ormore additional MSPDs on or in said single substrate, one or moreadditional active electronic circuits on or in the said singlesubstrate, and one or more additional communication channels configuredto supply electrical outputs from the MSPDs to the one or more of theactive electronic circuits.
 30. The single-chip device of claim 1,further comprising one or more additional active electronic circuitsthat are formed on or in the said single substrate.
 31. The single-chipdevice of claim 1, further comprising one or more additional activeelectronic circuits that are formed on or in the said single substrateand comprise one or more transimpedance amplifiers (TIAs) and one ormore application specific integrated circuits (ASICs).
 32. Thesingle-chip device of claim 1, further comprising one or more additionalactive electronic circuits that are formed on or in the said singlesubstrate and comprise one or more of CMOS, BiCMOS, and bipolar activedevices.
 33. The single-chip device of claim 1, further comprising oneor more additional MSPDs in an array on or in said single substrate andone or more additional active electronic circuits also on or in saidsingle substrate, said MSPDs and active electronic circuits beingconfigured into an optical communication structure or a light distanceand ranging (LIDAR) structure.
 34. The single-chip device of claim 1,further comprising a laser emitter formed on or in said singlesubstrate.
 35. The single-chip device of claim 1, further including alayer of selected material that is over a side of one of the first andsecond layers facing away from the intermediate layer and is configuredto reduce sheet resistance.
 36. The single-chip device of claim 1,further including a layer of selected material that is over a side ofone of the first and second layers facing away from the intermediatelayer and is configured to reflect light that has passed through theintermediate layer back toward the intermediate layer.
 37. Thesingle-chip device of claim 1, further including a deliberately texturedsurface at a side of one of said first and second layers facing awayfrom the intermediate layer.
 38. The single-chip device of claim 1,further including a layer of micro-nano structures formed at of one ofsaid first and second facing, at a surface thereof facing away from theintermediate layer.
 39. The single-chip device of claim 1, furtherincluding one or more distributed Bragg reflectors formed at one of saidfirst and second layers, at a surface thereof away from the intermediatelayer.
 40. The single-chip device of claim 1, further including anisolation trench between the MSPD and the active electronic circuit. 41.The single-chip device of claim 1, further including a light shieldlayer over said active electronic circuit.
 42. The single-chip device ofclaim 1, wherein the optical input and the electrical output are eachmodulated at a frequency of at least 30 Gigabits per second.
 43. Thesingle-chip device of claim 1, wherein the quantum efficiency of theMSPD that is at least 1.5 times greater than that of an otherwise samephotodetector that does not include said holes.
 44. The single-chipdevice of claim 1, further including a hermetic seal integral with thedevice.
 45. A microstructure-enhanced photodetector (MSPD) configured toconvert to an electrical output an optical input that in cross-sectionis essentially continuous spatially at least some of the time,comprising: a substrate and a top layer, a bottom layer, and anintermediate layer between the top and bottom layers formed on or in thesubstrate, wherein: at least one of the layers has holes intentionallyformed therein, extending in directions transverse to the layers; eachof the top and bottom layers comprises a doped material; theintermediate layer comprises a material that is undoped or is less dopedthan the top or bottom layer, wherein the degree of doping is the sameor different for different positions in the intermediate layer; an inputportion configured to receive, concurrently at a plurality of saidholes, said optical input that has said essentially continuouscross-section; and an output portion configured to provide saidelectrical output.
 46. The MSPD of claim 45, in which the top layer isno more than 500 nm thick and the holes are at least in the top layer.47. The MSPD of claim 45, further including an air-filled volume betweenthe substrate and the MSPD.
 48. The MSPD of claim 45, further includinga layer of a dielectric material that is at a surface of said substrate,over the holes and spaces between the holes, and in the path of saidoptical input.
 49. The MSPD of claim 45, further including an avalancheregion under the MSPD, forming therewith an avalanche microstructuredphotodiode (MSAPD).
 50. The MSPD of claim 45, in which said holes arepresent in said intermediate layer.
 51. The MSPD of claim 45, in whichsaid holes are present in said intermediate layer as well as in at leastone of the top and bottom layers.
 52. The MSPD of claim 45, in whichsaid holes are present in each of the top, bottom, and intermediatelayer.
 53. The MSPD of claim 45, in which each of said top and bottomlayers and said intermediate layer has a thickness and at least some ofsaid holes extend through the entire thickness of said intermediatelayer and of one of said top and bottom layers and through at least apart of the thickness of the other one of said top and bottom layers.54. The MSPD of claim 45, in which at least some of said holes areshaped as inverted pyramids.
 55. The MSPD of claim 45, in which at leastsome of said holes have triangular sections in planes transverse to saidlayers.
 56. The MSPD of claim 45, in which at least some of said holeshave triangular sections in planes transverse to said layers, withvertices within the intermediate layer.
 57. The MSPD of claim 45, inwhich at least some of said holes have sidewalls that slope in planestransverse to said layers.
 58. The MSPD of claim 45, in which at leastsome of said holes have sidewalls with plural different slopes alonginside walls of the holes.
 59. The MSPD of claim 45, in which at leastsome of said holes differ from each other in at least one of (i)distance by which the holes extend in said directions, (ii) shape of theholes, and (iii) spacing of the holes from each other.
 60. The MSPD ofclaim 45, in which the holes are in the intermediate layer and whereinone of said top and bottom layers conformally covers inside walls of theholes as well as spaces between the holes.
 61. The MSPD of claim 45, inwhich the holes are at least partly filled with a dielectric material.62. The MSPD of claim 45, in which the holes are entirely filled with adielectric material.
 63. The MSPD of claim 45, in which at least one ofthe top and bottom layers and the intermediate layer comprises amaterial represented by Ge_(x)Si_(1-x), where x is greater than zero butless than unity.
 64. The MSPD of claim 45, in which at least one of thetop and bottom layers and the intermediate layer comprises a materialrepresented by Ge_(x)Si_(1-x), where x is zero or unity or a valuebetween zero and unity.
 65. The MSPD of claim 45, in which said MSPDfurther comprises ohmic contacts configured for reverse-biasing theMSPD.
 66. The MSPD of claim 45, in which the MSPD further includes ohmiccontacts to said top and bottom layers, wherein at least one of saidohmic contact being through a via in said substrate.
 67. The MSPD ofclaim 451, further comprising a light guide to said MSPD for directingsaid optical input thereto.
 68. The MSPD of claim 45, further comprisinga light guide to said MSPD configured to bend the optical input from aninitial propagation direction to a propagation direction transverse toat least some of said layers.
 69. The MSPD of claim 45, furthercomprising one or more additional MSPDs formed on or in the singlesubstrate, and respective different optical bandpass filters coupledwith respective ones of the MSPDs, whereby at least two of said MSPDsare configured to respond to different wavelength ranges that are withinsaid optical input.
 70. The MSPD of claim 45, further comprising one ormore additional MSPDs in an array on or in said single substrate, saidMSPDs being configured into an optical communication structure or alight distance and ranging (LIDAR) structure.
 71. The MSPD of claim 45,further comprising a laser emitter formed on or in said singlesubstrate.
 72. The MSPD of claim 45, further including a material thatis over a side of one of the top and bottom layers facing away from theintermediate layer and is configured to reduce sheet resistance.
 73. TheMSPD of claim 45, further including a material that is over a side ofone of the top and bottom layers facing away from the intermediate layerand is configured to reflect light that has passed through theintermediate layer back toward the intermediate layer.
 74. The MSPD ofclaim 45, further including a deliberately textured surface at a side ofone of said top and bottom layers facing away from the intermediatelayer.
 75. The MSPD of claim 45, further including a layer of micro-nanostructures formed at a side of one of said top and bottom layers facingaway from the intermediate layer.
 76. The MSPD of claim 45, furtherincluding one or more distributed Bragg reflectors formed at a surfaceof one of said top and bottom layers facing away from the intermediatelayer.
 77. The MSPD of claim 45, further including one or more activeelectronic circuits formed on or in said substrate and coupled to saidMSPD to receive said electrical output therefrom and process it into aprocessed output, thereby constituting a single-chip integrated circuitconfigured to receive said optical input, convert it to said electricaloutput, and provide said processed output.
 78. The MSPD of claim 45,wherein the optical input and the electrical output are each modulatedat a frequency of at least 30 Gigabits per second.
 79. The MSPD of claim45, wherein the quantum efficiency of the MSPD is at least 1.5 timesgreater than that of an otherwise the same photodetector lacking saidholes.
 80. The MSPD of claim 45, further including a hermetic sealintegral with the MSPD.
 81. A method of making a microstructure-enhancedphotodetector (MSPD) configured to convert an optical input that atleast some of the time has a cross-section that is essentiallycontinuous spatially to an electrical output, comprising: providing asubstrate and forming on or in said substrate a top layer, a bottomlayer, and an intermediate layer between the top and bottom layers,wherein: at least one of the layers has holes intentionally formedtherein, extending in directions transverse to the layers; each of thetop and bottom layers comprises a doped material; the intermediate layercomprises a material that is undoped or is less doped than the top orbottom layer, wherein the degree of doping is the same or different fordifferent positions in the intermediate layer; forming an input portionconfigured to receive, concurrently at a plurality of said holes, saidoptical input that has said essentially continuous cross-section; andforming an output configured to provide said electrical output.
 82. Themethod of claim 81, in which the step of forming the top layer compriseslimiting the top layer to a thickness of no more than 500 nm, and thestep of forming the holes comprises forming the holes at least in thetop layer.
 83. The method of claim 81, further including forming anair-filled volume between the substrate and the MSPD.
 84. The method ofclaim 81, further including a layer of a dielectric material that is ata surface of said substrate, over the holes and spaces between holes,and in the path of said optical input.
 85. The method of claim 81,further including forming on or in said substrate an avalanche regionunder the MSPD, forming therewith an avalanche microstructuredphotodiode (MSAPD).
 86. The method of claim 81, in which forming saidholes comprises including the holes in said intermediate layer.
 87. Themethod of claim 81, in which forming said holes comprises including saidholes in said intermediate layer as well as in at least one of the firstand second layers.
 88. The method of claim 81, in which forming saidholes comprises forming the holes in each of the top, bottom, andintermediate layer.
 89. The method of claim 81, in which each of saidtop and bottom layers and said intermediate layer has a thickness andthe forming of the holes comprises extending the holes through theentire thickness of said intermediate layer and of one of said top layerand bottom layer and through at least a part of the thickness of theother one of said top and bottom layers.
 90. The method of claim 81, inwhich forming of the holes comprises forming at least some of said holesin the shape of inverted pyramids.
 91. The method of claim 81, in whichat least some of said holes have triangular sections in planestransverse to said layers.
 92. The method of claim 81, in which formingthe holes comprises forming at least some of said holes with triangularsections in planes transverse to said layers, with vertices within theintermediate layer.
 93. The method of claim 81, in which forming saidhoes comprises forming at least some of said holes with sidewalls thatslope in planes transverse to said layers.
 94. The method of claim 81,in which forming said holes comprises forming at least some of saidholes with sidewalls that have plural different slopes along insidewalls of the holes.
 95. The method of claim 81, in which forming saidholes comprises forming at least some of said holes such that theydiffer from each other in at least one of (i) distance by which theholes extend in said directions, (ii) shape of the holes, and (iii)spacing of the holes from each other.
 96. The method of claim 81, inwhich forming said holes comprises forming at least some of the holes inthe intermediate layer and forming said top and bottom layers comprisesforming at least one of the top and bottom layers to conformally coverinside walls of the holes as well as spaces between the holes.
 97. Themethod of claim 81, including at least partially filling the holes witha dielectric material.
 98. The method of claim 81, including completelyfilling the holes with a dielectric material.
 99. The method of claim81, in which forming the layers comprises forming at least one of thetop layer, the bottom layer, and the intermediate layer of a materialrepresented by Ge_(x)Si_(1-x), where x is greater than zero.
 100. Themethod of claim 81, in which forming the layers comprises forming atleast one of the top layer, the bottom layer, and the intermediate layerof a material represented by Ge_(x)Si_(1-x), where x is zero or unity ora value between zero and unity.
 101. The method of claim 81, furthercomprising forming ohmic contacts configured for reverse-bias the MSPD.102. The method of claim 81, further comprising forming a light guide tosaid MSPD for directing said optical input thereto, said light guidebending the optical input from an initial propagation direction to apropagation direction transverse to said layers.
 103. The method ofclaim 81, further comprising forming one or more additional MSPD on orin said substrate for receiving respective optical inputs, and formingrespective different bandpass filters for said optical inputs, therebyconfiguring different MSPDs on said substrate to respond to differentwavelength ranges that are within said optical input.
 104. The method ofclaim 81, further comprising forming one or more additional MSPDs in anarray on or in said substrate, said MSPDs being configured into anoptical communication structure or a light distance and rangingstructure (LIDAR).
 105. The method of claim 81, further comprisingforming a laser emitter on or in said substrate.
 106. The method ofclaim 81, further including forming a layer of selected material that isover a side of one of the top and bottom layers facing away from theintermediate layers and is configured to reduce sheet resistance. 107.The method of claim 81, further including forming a layer of selectedmaterial that is over a side of one of the first and second layersfacing away from the intermediate layer and is configured to reflectlight that has passed through the intermediate layer back toward theintermediate layer.
 108. The method of claim 81, further includingdeliberately texturing a surface at a side of one of said top and bottomlayers facing away from the intermediate layer.
 109. The method of claim81, further including forming a layer of micro-nano structures formed atof one of said top and bottom layers, at a surface thereof facing awayfrom the intermediate layer.
 110. The method of claim 81, furtherincluding forming one or more distributed Bragg reflectors at one ofsaid top and bottom layers, at a surface thereof away from theintermediate layer.
 111. The method of claim 81, further includingforming, on or in said substrate, one or more active electronic circuitsconfigured to process the electrical output from the MSPD into aprocessed output, thereby forming a single-chip integrated circuitconfigured to receive said optical input, convert it to said electricaloutput, and provide said processed output.
 112. The method of claim 81,further including hermetically sealing the MSPD with a coating integraltherewith.